Plan B

Alright girls, hear me out cause I am very uneducated on the topic. So my boyfriend and I were fooling around the other day and he was rubbing his head against my vagina, there was no actual sex, just the tip I think. Anyways, while rubbing against me he didn't pull away 100% in time and he said it was possible he came a little on me. However, I didn't feel anything when I touched down there. I took plan b a few hours later just in case. My question is: it's impossible for me to get pregnant, right? 
Thanks girlies!