Should I be worried?

Ok so I'm a paranoid person. My BF and I were having sex, the condom was fine but hurting him, so we took it off and I finished orally. However, I hate the taste of cum, so when he was about to cum I rolled over onto my stomach and he came on my back. He kind of missed and got a little on my butt (like in the crack). I'm worried it could somehow have gotten into me? I checked and I am not sure if there was cum near my vagina or if it was just the usual stuff. My period ended like 2 days ago so I'm not ovulating or anything either, but do you think I'm pretty good? I really don't want to take plan b, but I'm soooo paranoid. Thanks!