Heivin, 18, confirmed the boat was stormed by a rival group of migrants, armed with sticks and knives, as it was preparing to set off.
She said: "People were fighting, people were getting stepped on, they were dying and being thrown off."
She said she fell into the water but was pulled out by another person on the boat. Two other passengers who fell into the water, including a young girl, drowned. Three other people died on the boat.
Heivin said she "really hated" the group of people who hijacked their boat, insisting they should take the blame for what happened.
"They caused a huge tragedy," she said.
"It was because of them that people died.
"If they hadn't come and started fighting, none of this would have happened."
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The tragedy happened in the early hours of Tuesday morning in the waters off the French coastal town of Wimereux.
The boat, which launched with 112 people on board, stopped on a sandbar only a few hundred metres from the shore.
By the time emergency services arrived, it was clear people had died, both on the boat and in the water.
"I fell into the water but a man helped me up," Heivin said.
"Everyone was climbing aboard and there were too many people - over 110 of us.
"I had tried to be at the front, but after I fell in the water I sat on the edge of the boat and didn't go towards the other end - that's where people were fighting.
"I thank God that I didn't get into the top part of the dinghy. I would have suffocated. I thank God for that every day."
She said her group, comprising between 50 and 60 people, had arrived at the beach in Wimereux after following the instructions of the people smugglers who had taken their money in exchange for arranging a passage to Britain.
Hidden away, they had waited for the smugglers to prepare the dinghy. She then saw police officers and was told simply to run towards the water.
At that point, the rival group emerged as well, clambering into the boat along with the people who had paid the smugglers.
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Heivin said she saw migrants from this group carrying sticks and knives, squaring up to both the police and the original passengers.
When the boat set off, exceptionally overladen, it meandered towards the Channel, but there was still fighting and it is clear that some people were being crushed.
"I was aware there was a fight," Heivin said.
"They were shouting that people were stuck underneath other people, that they couldn't get out, that some were falling under people's feet."
Heivin has spent seven months travelling across Europe since leaving Iraq. She said she wanted to get to Britain because "it is a better country for me, definitely in terms of the language but also, in many other other ways, it is better than the rest of Europe".
She's made 30 attempts to cross the Channel, but has failed each time. Sometimes it has been the French police who have destroyed boats while other times the boat on which she was travelling broke down. One time, the boat failed only an hour from British waters.
She is undeterred by the trauma that she underwent, however, and she intends to try again to reach Britain as soon as possible. "Perhaps this weekend," she said.

The Rwanda Bill, which will see asylum seekers "entering the UK illegally" sent to the central African nation - regardless of the outcome of their application - was passed on Tuesday, despite human rights concerns.
Micheal Martin told The Daily Telegraph that the policy was already affecting Ireland, as people were "fearful" of staying in the UK.
The former Taoiseach said: "Maybe that's the impact it was designed to have."
Mr Martin, who is also Ireland's foreign secretary, said asylum seekers were seeking "to get sanctuary here and within the European Union as opposed to the potential of being deported to Rwanda".
His words follow those of justice minister Helen McEntee, who told a scrutiny committee in the Irish parliament earlier this week that migrants and refugees were crossing the border with Northern Ireland.
Ms McEntee said "higher than 80%" of people seeking asylum in Ireland entered the country through Northern Ireland, a border crossing that is open as guaranteed under a UK-EU Brexit treaty.
It comes amid increasing tension over immigration levels in Ireland, which is grappling with a housing crisis that has affected its own people as well as asylum seekers.
Overnight, six people were arrested during a protest at a site earmarked to house asylum seekers in Newtownmountkennedy in Co Wicklow.
Gardai said officers came under attack after workers were brought onto the site, suffering "verbal and physical abuse throughout the day, which escalated into rocks and other missiles being thrown this evening".
Fires were lit, an axe was found and officers were "forced to defend themselves" with incapacitant spray, helmets and shields.
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Three patrol cars were also damaged.
Irish broadcaster RTE said protesters accused gardaí of using unnecessary force, and intimidating and aggressive tactics against a legitimate and peaceful protest.
According to RTE, there have been protests during the past six weeks at the site, known as Trudder House or River Lodge.
It is reportedly being considered as a site for 20 eight-person tents housing asylum seekers but some locals have said it is unsuitable and the village's resources are already over-stretched.
Ms McEntee said there was "a lot of misinformation about migration at the moment".
She tweeted late on Thursday to promote the EU Migration and Asylum Pact, which she described as "a real game changer" and "something we must opt into".

He has got his flagship Rwanda bill through parliament and is promising a "regular rhythm" of flights will be getting off the ground from July.
He has also got off the ground himself, with a dash to Poland and then Germany, in a show of strength with European allies in the face of Russian aggression.
As the US finally approved a $61bn military aid package for Ukraine, our prime minister announced he'd lift the UK's defence spending to 2.5% of GDP by 2030.
That would amount to £87bn a year by the start of the 2030s, with the UK spending a cumulative extra £75bn on the military over the next six years.
That of course all hinges on winning an election, which I'll come to soon, but it is a commitment that throws a challenge to Labour and will delight those in his party who have been calling for increased defence spending for months in the face of growing global threats from Russia, China and Iran.
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In Electoral Dysfunction this week, we discuss whether Rishi Sunak, having been battered for much of his premiership, is finally having a week on top?
There is after all a longstanding tradition in this country that when the chips are down, you jump on a plane to try to go somewhere where you're more appreciated.
And Ruth agrees this week that this has been "one of the better weeks that he's had in his premiership" and is fully behind his defence spending pledge, while Jess points out that Labour is committed to the "exact same plan for upping defence spending".
The difference between the two parties is that Rishi Sunak set out in some detail how he plans to get to that point over the course of the next parliament, while Sir Keir Starmer has said only he wants to get to 2.5% "when resources allow".
And that matters because, as it stands, it's very likely that it will be Sir Keir who is having to decide whether to increase defence spending levels in the next parliament rather than the incumbent.
Cue an election debate on which leader really cares more about defence and, if Sir Keir really does want go toe-to-toe with Mr Sunak on the 2.5%, how does he pay for it?
That will be a discussion for many other days (Labour's line on this is that the party will hit the 2.5% "when circumstances allow" rather than setting a firm date) as we head into the general election.
But I had to ask Ruth and Jess, why was he on a publicity blitz announcing it now? Was it something to do with the rather large matter of the local elections?
'Sunak needs to look big'
At this, both furiously shook their heads and looked at me with a touch of derision. "When it comes to the local elections, I want my bins done, I want my schools to be good, and I want my potholes done. That's what I care about," says Ruth.
"The people in Birmingham Yardley speak of nothing else but the 2.5% defence spending," jokes Jess.
"I see why [he's doing it this week] but actually I don't think he's doing for just another example of doing it this week. He needs to look big in front of his party."
And there are a couple of things to explore in that.
First, the party management issue of a PM very likely to get completely battered in the local elections throwing his party some red meat ahead of that slaughter to perhaps try to protect himself.
Because the local elections could be bad, very very bad. And that throws up questions about Rishi Sunak's future and also the date of the next general election.
There is a reason why the prime minister will not be drawn on the timing of the election beyond the "second half of the year".
While it's true he doesn't want to have to "indulge in a guessing game", as one of his allies put it to me, it's also true that he can't rule out a summer election given the unpredictability of next week's local elections and what could follow.
The Armageddon scenario of losing 500-plus seats, alongside the West Midlands and Teeside mayors, could propel his party into fever pitch panic and possibly trigger a vote of confidence in Rishi Sunak.
Does he then decide to call a general election instead of allowing his party to try to force him out?
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'A man enjoying himself'
For what it's worth, he did not appear, in any way to me, as a prime minister on that plane over to Berlin from Warsaw, who wanted to give up the job. He seemed, for the first time in a long time, a man enjoying it and getting on with the stuff he wants to get done.
There is also the small matter of being 20 points behind in the polls. I suspect his instinct is very much to hold on in the hope that things begin to turn in his favour.
Because, despite what the critics say, he does seem a man who genuinely believes his Rwanda plan, welfare reforms, defence spending and economic management are all stepping stones on his path to perhaps winning back some support in the country.
"June [or July] is just party management," says one former cabinet minister. "They are not ready for it and the polling doesn't work obviously."
Jess sees the flurry as a "his last ditch attempt" of another reset, and says "the Labour party is not worrying" as the PM tries to pin them on Rwanda or defence spending: "Whatever he goes on is absolutely pilloried within seconds," she says.
But Ruth argues the defence spending was "actually authentic and a real thing", and says of the expectations for the local elections that "it's not just going to be a rout, but an apocalypse, that actually at this point in the cycle it works quite well for Sunak in terms of keeping his job at the back end".
Observing his various grip and grins this week as I trailed after him meeting the Polish PM, the German chancellor and the NATO secretary general, he is a man that really does want to hold on to that job.
The local elections then are probably going to come as a horrible reality check in just a week's time as this prime minister, riding high from his European tours, is reminded that his time in office looks like it will be coming to an end - and perhaps even sooner than he might have initially planned.

The "gamechanger" jab also has the potential to stop bladder, lung and kidney cancer.
It's custom built for each person and tells the body to identify cancer cells and stops the disease returning.
A stage-two trial found it significantly reduced the risk of cancer coming back in melanoma patients and now a final trial has been launched.
University College London Hospitals NHS Foundation Trust (UCLH) is leading the phase.
Dr Heather Shaw, co-ordinating investigator of the trial, said it was "one of the most exciting things we've seen in a really long time".
"This is a really finely honed tool," she said.
"To be able to sit there and say to your patients that you're offering them something that's effectively like the Fat Duck at Bray versus McDonald's - it's that level of cordon bleu that's coming to them.
"These things are hugely technical and finely generated for the patient. The patients are really excited about them."
The jab is an individualised neoantigen therapy (INT) and can trigger the immune system to fight the patient's specific type of cancer.
To create the personalised therapy, a tumour sample is removed and has its DNA sequenced - with artificial intelligence also playing a role.
Dr Shaw said: "This is very much an individualised therapy and it's far cleverer in some senses than a vaccine.
"It is absolutely custom built for the patient - you couldn't give this to the next patient in the line because you wouldn't expect it to work."
She added: "I think there is a real hope that these will be the gamechangers in immunotherapy."
The aim is to ultimately cure the cancer and eradicate any rogue cells that might not show on scans.
The phase-two trial found people with high-risk melanomas who got the jab - alongside immunotherapy drug Keytruda - were about half (49%) as likely to die or have their cancer come back after three years than those who just had Keytruda.
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The phase-three global trial will include a wider range of patients and researchers are hoping to recruit around 1,100 people.
At least 60 to 70 patients across eight UK centres are set to be recruited and the twin therapy combination will also be tested in lung, bladder and kidney cancer.
Professor Lawrence Young, from the University of Warwick, called it "one of the most exciting developments in modern cancer therapy".
"Interest in cancer vaccines has been reignited in recent years by a deeper understanding of how the body controls immune responses and by the advent of mRNA vaccines which makes developing a vaccine based on the immune profile of a patient's own tumour much more straightforward," said Prof Young.
"The hope is that this approach could be extended to other cancers such as those of the lung and colon."

Outside the port city of Ningbo, Chinese car company Zeekr is rolling out luxury EVs and growing fast. The factory has only been up and running for three years, but this year it's more than doubling production.
Zeekr is a new player in the EV market, but it has unbridled ambition to sell its high-end, high-tech cars abroad. It's a subsidiary of a state-backed company, Geely.
However, US and EU critics say the financial backing and vast resources of China's government gives companies like Zeekr an unfair advantage.
In a recent trip to Beijing US treasury secretary Janet Yellen accused China of "overproduction" and "dumping" its EVs on overseas markets. The European Commission has started an investigation into whether to impose punitive tariffs on China's industry.
But at Zeekr the threat of tariffs is being talked down. The company insists the global market is big enough for everyone.
Speaking to Sky News at a massive auto show on the outskirts of Beijing, Zeekr vice president Chen Yu explained that when foreign car companies first started setting up EV plants in China, local car companies watched on and learned fast.
"Definitely," Mr Chen said. "We learned about the performance, the design, the culture, everything."
Now companies like Zeekr, and BYD which is a giant in the Chinese EV manufacturing market, are taking on traditional car companies.
"I would not say (Chinese EVs) are dominating the market. I would say just they bring more diversity to the local customer, that is the nature of competition as you know," Mr Chen said.
However, the possibility of Europe slapping tariffs on Chinese EVs is a concern for the Zeekr executive: "Definitely, if the tariff goes up, no doubt we are worried about the potential challenge."
On the floor of the auto show, car dealers and importers were clearly impressed with China's EVs and warned legacy car manufacturers that they are in trouble.
New Zealand car dealer Matthew Foot has been attending the annual show for five years, and said: "It's going to be very hard to beat China. They get incredible resources from the government; from lithium mines, to the ships and everything in between.
"Obviously you can see why Europe is fearing them and taxing them as well."
This week US Secretary of State Antony Blinken is in China. Trade tensions are on the agenda, alongside the world's geo-political crises.
The US already imposes a 27.5% tariff on Chinese cars. But in Europe it's only 10% and that makes companies like VW, Volvo and BMW increasingly nervous.
In Beijing last week German Chancellor Olaf Scholz said: "It's clear that we have to talk about questions of overcapacity, and that we have to talk about subsidy competition."
Germany is in a difficult position. As Europe's largest car manufacturer, it fears that if the EU slaps tariffs on Chinese cars, China could retaliate by restricting access to its vast market.
But the fact is, more than half of all new electric cars sold worldwide are from China and it can make them cheaper and faster than its competitors.
At the end of last year China's EV giant, BYD, sold more electric cars than Tesla. Tesla was back on top last quarter, but the competition is fierce.
The scale of production is staggering. BYD owns its mines, battery factories and eight ships.
Even a comparatively smaller company like Zeekr is the model of efficiency, with 2,700 workers churning out around 500 cars a day.
The focus on EVs is part of Chinese President Xi Jinping's plan to overhaul the country's debt-driven economy. He calls it "new production forces". Investing in infrastructure is out, new technology is in.
In the industrial hub of Anhui Province, local officials are also brushing off the looming threat of tariffs. Provincial official Pan Feng said: "Some countries, thinking about their short-term self-interests, introduced some regulations, but I think they are only temporary.
"China is a big country, with a big market, it has huge power and confidence to counteract these conflicts."
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Chinese buyers are also confident about their country's electric cars, purchasing more than seven million of them domestically last year.
The country also has more charging stations than anywhere else on the planet.
While charging his BYD electric car in Zhejiang Province, Mr Chen told us: "Chinese-made cars are good enough for us ordinary Chinese. If you're thinking of buying an EV, there's no need to go for a Mercedes or a German EV."