I need answers

So i recently had sex for the first time a week ago we didn’t use protection but he only stuck in the top because we got interrupted, he says he doesn’t know if there was “pre-cum” when he went to stick it in and now I’m scared that I could be pregnant, my mom says I should be fine but I still haven’t gotten my period and I just want to know if I should go buy a test or just wait and see if I get my period considering it was my “first time” someone please help