The answer to this question is entirely dependent upon the nature and extent of the discrepancy. The fact that there may be a discrepancy between what you said at the time of the accident versus what you are now saying is not by itself case determinative. In other words, there are many other factors that likely matter more such as what other witnesses say and what the physical evidence shows. In addition, the fact that your memory conflicts with what you initially said may have no relevance, may have some relevance or maybe entirely relevant.
Its relevance and impact depend upon whether the conflicting statements were meaningful or not. The fact that the statements may not be exactly the same is to be expected. If major facts are different and even the opposite, then it can impact whether you prevail or lose your case.
If you said the light was green and later said it was red and the color of the light is determinative of who is at fault, then yes, it will impact your case. It does not necessarily mean you will win or lose the case but it likely would have an impact. In the end, a trier of fact (such as a jury or arbitrator) decides how much your conflicting statements matter.
A trier of fact may think your conflicting statements are not an issue or a trier of fact may determine your conflicting statement is determinative of your case. In the end, a trier of fact will weigh your statements along with other evidence in the case to reach a determination.
Remember, personal injury law can be extremely complex. Make sure you have the right law firm representing you. It will make all the difference in your claim.