what do I do?

I’m 17 and not quite “sexually active” I’ve only had sex one other time. Last night it happened completely unexpectedly and I made a dumb mistake of not knowing if he had on a condom or not . I asked him after and he said he did but I’m still paranoid because I didn’t see it. I can’t afford a plan b and I CAN NOT tell my mom or any adult close to me . How can I tell if he had one on or not ? What do I do?