Losing my virginity

To me,virginity was never a thing to worry about. I am F(18) and last night i did it with a guy that I've hung out with once before,him saying he just wants to be fwb is okay w me. And so we did it in his car with a condom but while doing doggy,once he finished he took it off and threw it away,he told me ,,i took it off because we have another one",and i was sitting there minding my own business, everything was fine and then i sucked him off and he came in my mouth. For some reason, now while talking to my friend about it,i kinda became paranoid that i might get pregnant, somehow. My fertile window ended today,yesterdays chance of pregnancy was at 8% and my period is supposed to come in 12 days. Do i buy plan b and take it today? What should i do in general

Please help your girl out.