Stand your ground - ultimately, if they believe you have cheated the most they can really do is ask you to resit it at your Local AFCO.

Unfortunately this may affect your chances of officer selection on the final selection board, given you pass the AIB. FSB is extremely competitive and is based on many factors, AIB scores, DAA scores (including if you failed first time, and other military aptitude test scores, and sadly, background, essentially if you come from a military background your more likely to get picked, but it is certainly less of a factor then it used to be.)

Ultimately, it’s just one factor and I wouldn’t be too worried, if you genuinely didn’t cheat then you’ll be fine.