pregnant?? help!!

fuck im freaking out i hooked up with this guy today and he had a condom on but i guess at some point he took it off without me knowing and he didn't cum inside me but i know you can still get pregnant. i was hella mad and he tried to act like it slipped off or something but im not a fucking idiot. im getting plan b tomorrow from a friend and im on birth control but im on antibiotics (amoxicillin) so idk if that fucks up my birth control 😭😭😭 im only 17 i can't get fucking pregnant. my period is in 8 days. idk what should i do?? do u think my chances are high? advice on what to do? should i take a pregnancy test?