Could use some advice!

Okay so help a girl out. My partner and I had sex this morning and the condom came off and got stuck in me and he doesn't know if he came inside of me or not. No worries we got the condom out, but it was like deep inside me. But we are assuming he did one in me. So, my question is should I take plan B or not? I've been on birth control for almost two months now and I haven't missed a day, and I've only been late two days, both of them I was only 2-2.5 hours late in taking it. The last time I was late was two weeks ago. So I think I should be good, but I'm just seeing what you guys think. I was just wondering if I need to take plan B to be extra safe, or would it be a waste of my time? Also, I'm 5 days away from my placebo pills so would taking Plan B mess with my period and get my birth control off track?