When I was filling out my pre-app for NASS I wasn't sure of my class rank. and pretty much guessed. I just recently found out my class rank is much higher, will this mistake affect my actual application?
Ultimately I believe the class rank has to be certified when the counselor certifies the transcript. I wouldn't think it would be a huge deal since it was originally an estimate. My DS' estimated class rank back in February came to him on a sticky note.
No, I don't think it will matter. Self-reported information for the NASS application is different from the official USNA application which includes information your school has to provide.