My boyfriend accidentally came inside of me. I was on the last day of my period and he said it was only a little bit. Could I be pregnant?

You could be. There is a little room for error in this "rhythm method" thing.

You sure could be. Get a morning after pill and from now on use a different form of birth control.

How the hell did he get all the way inside you???

It is unlikely as you do not ovulate when on your period. Usually ovulation occurs mid cycle for 2 days and you could still get pregnant 2 days before and after ovulation cause sperm can live for up to 48 hours.
But weirder things have been known to happen. If you really don't want to get pregnant, go on the pill or start using condoms. Sperm are fighters. Your doctor is supposed to maintain confidentiality so he/she cannot tell your parents. And tell him you want your confidentiality maintained. The pharmacist should maintain your confidentiality though it could slip. You could go to one your parents do not use. The condom is a good option if you don't want to take the pill. Why take the chance, he is bound to slip up again. Also you can still get pregnant from pre-ejaculate so the withdrawal method really isn't safe at all.

its it safe like until 5days after periods..we never use any sort of protection 5days after my periods. Although like nada suggested take the morning after pill.

I doubt it, but then again, I'm not a doctor.