I did not say that one should always include "got". However, in this case, it seems to be better than without. "You do not/don't have a chance" would have been fine (nobody would add "got" here). "Not a chance" on its own is an idiom , and is fixed, so one would not add "got" here either (http://dictionary.cambridge.org/dictionary/english/not-a-chance). However, based on some research, "I have not a chance", seems to be used by natives, and is considered "informal" (which does not mean it's incorrect). Once again, I did not say your answer was wrong, I only said "'You haven't GOT a chance' would make more sense" in this case. At the end, the top comment encourages the Duolingo team to accept "you haven't got a chance", which has been liked by 12 individuals, so perhaps one day they will accept both suggestions.