I messed up

So I’m a virgin and so is my boyfriend. I’ve always said I never wanted to do anything because I don’t want to get pregnant. Well yesterday me and him got caught in the moment and it happened with out any protection. He didn’t cum in me he did it on my stomach but I’m scared there is a chance it started dripping down because I do know some of his cum got on the sofa. I looked at my fertility and yesterday it was at its peak. I’m really scared and I don’t know what to do. Please don’t judge me I know it was very stupid. I am gonna take a Plan b but is that even going to work?