I Am Afraid Please Clear My Doubt. Last Week Me

I am afraid Please clear my doubt. Last week me and my boyfriend were fooling around. He ejaculated and some semen got in my back. I went to wash it immediately with water and while doing so I had my underpants on. I am pretty sure that nothing entered inside my vagina not even the water. But is there amy chance that the sperms can penetrate through the underpants and get me pregnant?