I definitely feel bad for you because of the mistake you made- unfortunately this is an integrity issue. Schools may not find out while the're reviewing your application, but once you decide to accept an offer from a school, you'll have to send official transcripts from all your schools directly to them- so no matter what, they'll find out and if they find out after the fact- they may be so upset they'll take away the offer from you. So, maybe the best thing is talk to the registrar's office and see if there is a way to correct the mistake, talk to the prof if u remember them. And best thing call the schools you are interested in and see what you can do. good luck with this ethical delimma