took plan b

So I think the condom we were using mustve been a little too big.. because it slipped off and we didn't notice until I felt something hot as he was pulling out! I don't know if it was inside and i dont think it was my fertile period.. I got really scared and he bought me plan b. I feel bad because it's so expensive though, and I'm not sure if it was necessary. Was that the right thing to do? I'm not looking forward to the side effectss