comments on my practice exams and section bank and histidine question

Hello everyone, I've taken 8 TPR full length exams ranging from 498-502. I took the non-scored AAMC (which scores on percent correct): 66% physical, 66% CARS, 83% bio, 76% psych. Section bank: 70% on all sections AAMC question pack bio1 66%, bio2 80%, physics 76%, chem 82% Exam is september 1st, thinking about taking the scored AAMC tomorrow. also.. is histidine neutral or charged at a PH7. i've seen multiple people post, some say neutral, some say positively charged, can someone let me know for sure?

Thanks guys aiming for 508