ladies help. I've never had this problem. I don't know what to do now

Heather
I had sex Thursday morning. I am avoiding pregnancy. I am 18 and my periods are regular.. I was ovulating by Glow calendar, and thinking back my boyfriend finished on my back and put his dick back in me.. then remembering the white stuff in me was not my own... what do I do it's too late for Plan B and he is no help saying he doesn't remember. I am trying to stay calm. I really don't wanna be pregnant my senior year.. what are the chances I could be pregnant from the "re-imsemination".. ahh ladies please keeps my spirits high I'm very nervous that there might have been cum inside me now.