Hey! You won't be able to change it and I would recommend not pointing it out unless asked. If your understanding is native that's probably close enough so that interviewers won't bat an eye. You're likely more advanced than plenty of applicants who mark 'advanced' as their fluency level.
If they do ask, just explain the way you did here. You'll be ok, best of luck!
I respectfully, but vehemently, disagree, and would love someone like @
LizzyM or
@gyngyn to either agree or disagree with me.
The danger in leaving it alone is the risk of being outed during an interview by an interviewer who might want to test the representation. If that happens (I'm not sure how high the risk is, but it's certainly >0) I think it will be too late to say "mistake" at that point, as opposed to now. For the record, fluent is very different from advanced, and it will be obvious to anyone with advanced skills whether or not someone else is fluent. Also for the record, I have many, many years of training in a language, certifications, etc., and am pretty damn close to fluent, but I am not a native speaker and didn't dare claim fluency, because it isn't necessary to demonstrate my proficiency and because I am not truly fluent. Of course, YMMV.
@kokoriko is correct insofar as you cannot quietly go back into AMCAS and change it, so sending everyone an update or e-mail to correct the misrepresentation will surely be embarrassing, but I think the consequence of not doing so and maybe being caught later will be worse if someone actually decides to test you, since it's a very easy thing to verify. I also think it would be quite awkward to clarify at the beginning of every interview, and therefore far better to just do it in writing now and get it over with, even at the risk of turning some people off.