Tmi about sex please help

Me and my SO had sex today, and the condom came off just as he finished, but the condom was stuck inside me and some semen dripped out onto my butt,I'm wondering if I should get a plan B just in case, I just had a baby 2 1/2 weeks ago, I'm not trying to get pregnant again, I'm planning on going onto birth control after my check up in 2 weeks. It didn't break or anything.