I need help. Please.

I started my period yesterday. Usually the first day I’m on my period I’m really heavy. My period only lasts for abt 4 days and I’m really really light everyday except the first day I get it. My boyfriend and i did “it” today and we didnt use protection, like idiots, I know. And he pulled out but he said there was some that was really really close to my vaginal area but he didn’t see any go IN. Idk what to do. I’m thinking I’m going to get Plan B tomorrow morning. Any advice? Please don’t hate or leave rude comments I understand that we were being dumb.