Unless there is some
unique circumstance that hugely impacted your MCAT prep, or if there was something that happened at your test center during your test that you filled a report to the AAMC about, then I would probably not mention it in the additional information section. Are you going to reveal something that makes them think, "Oh, man. We weren't going to interview this applicant, but now we are for sure"? Cuz if not, I would just wait to see if they ask you about it during an interview or if you find a way to naturally mention something about it at the interview if you think it is needed. It sounds like based on the other aspects of your application, you got a great shot at getting an interview! So I wouldn't draw unnecessary attention to your MCAT in the additional information section that is optional. They gonna see it, and it ain't a show stopper by any means! I mean look at the MSAR data below. A whole quarter of the enter class scored a 505 or lower. That means it is very common to get in with that score.
View attachment 314196