Plan b

Ok I'm getting scared now. On the 3rd day of 5 of my period  me and my boyfriend we messing around in a high chemicaled hot tub and he thought he got pre cum in me so I took plan b two days later. I'm not 6 days late today. And idk if I should take a pregnancy test or not. I've read about plan b and it's says everyone reacts differently but it really messes with your cycle. I'm only 18. And I really scared.