Plan b?

Deanna
Okay, I was on birth control for about three years and I stopped taking it about a year ago because I wasn't having sex so I saw no need for it (I wasn't in a relationship) I recently have tried to start up again as I'm in a relationship now and I could never get on a proper schedule as I work nights and went to school. Since schools ended I've gotten on a really good schedule with my pills and I've been taking them regularly for the first week and a half so far (yes I know that's not much protection) but getting to the point, my boyfriend and I had sex last night and he was inside me without a condom and before he finished he put one on and finished in the condom (sorry that's graphic lol) I know there's a chance of pre cum having sperm in it and that freaked me out so I went and bought plan b.. 
My question is, should I take the plan b just to be safe ? Or will it cancel each other out and increase my risk of pregnancy ?
Thanks so much for answering !