Should I be worried?

Farcia • don't be fucking rude
Okay, so my period started on Saturday the 8th. My boyfriend and I had unprotected sex on Sunday the 9th (the second day of my period). He came inside of me and told me not to worry because I'm on my period. Naturally, I started to worry so I took a Plan B on Monday (the 10th) morning. Would there even be a chance of me getting pregnant? Also, how will Plan B affect my next period? 
(ALSO, I know having unprotected sex isn't the smartest idea but everyone makes mistakes..)