Everyone makes mistakes, we all are human. Unless you continue to make these mistakes on a day to day basis you will be fine, just be more careful. It's good to have sense on urgency while being a cashier but in the end sometimes it's better to just take it a little slower so you don't over scan something or mis scan something. Apologize to the AP, let them know it wont happen again and you promise to be very careful, if you want let them know you were working with sense of urgency and made those mistakes.You will be careful next time and it wont happen again.
Ive made mistakes too. Although i'm not cashier, I work as a PA and a few times ive made typos in the zebra when charging out outdated bread, one time i had 2 outdated bread packages on the bakery table and accidentally i typed 12 and pressed process. and it was too late. I was like OMG FACEPALM. It's happened other times too but I try to be careful. Don't we all make typos?
Btw when that does happen anyone know if theres a way you can fix that so the quanities are accurate? (sorry for changing the subject)