Can you get pregnant 2 days before your period is due to come

Tiffany
Its 2 days before my period technically 1 day before since its almost midnight and My boyfriend and I had unprotected sex..... He didn't pull out quick enough and I'm certain some semen came in me..... What is the percentage for chance of pregnancy 2 days before my cycle starts? Should I just go purchase a Plan B to be on the safe side?