Plan B?????

I'm 22 years old and my fiancé and I had unprotected sex last night (Edit: I ended my period yesterday). We were caught in the moment but we talked about it being risky. We are always careful and always protected, but he went in bare for literally a minute but pulled out (caught in the moment but we knew it was risky). He said he was trying to hold it in (pre-cum). We didn't continue (was worried) and he didn't finish inside of me, but I've read about how pre-cum can still be slightly possible to get pregnant. Should I take Plan B to be 100% sure? Thanks for your advice in advance!