Factual error: Immediately after Eddie surfaces following his dive, he rests with his head well above the water. Had he actually been in water deep enough for the dive, he would have floated with his chin about even with the surface.
Factual error: Eddie claims it takes 30s for the drug to take effect. Tablets/capsules do not work within 30 seconds after ingestion. At most, 15mins is the time a drug can be absorbed into the body. This is also noted in the movie reviews.
Factual error: During the shootout in the apartment, the blinded henchman fires his handgun 24 times before reloading (and about the same afterwards). Only small-calibre pistols would have that capacity, and the gun he's using isn't one (either to look at and from the bullet holes it causes).
Suggested correction: The main character says he did quintuple his money four days in a row, not that he could continue to do so. "Presumably" he could do anything, like robbing a bank. Gambling is not a secure source of income, even with knowledge of the odds and every tell, he could also lose a lot of money.
He takes the seed money and then goes on to make a couple million with it on the stock market. There's really no reason he couldn't have just done that with the $800 seed money (also what the hell happened to that $10-20k stack of cash he took from Vernon's apartment? Somehow that was dwindled down to only $800?). The time constraint was totally artificial. He didn't need to conquer the world in 2 months except for the needs of the plot.