Sex Induced Period?

So my boyfriend and I had unprotected sex (not smart, I know) on Monday night, no more than 5 minutes and he did not ejaculate. Afterwards, we noticed spotting from my period which was supposed to come on Wednesday. So the next morning (Tuesday) I've started my regular cycle. I just want to know, should spend the money to take the plan B pill since we are not trying to get pregnant right now (oh and according to Glow, I had only a 3% chance of pregnancy) or should I hold off? Thanks ladies!