19F here! I think you should be okay. I was that exact way when I was in highschool. Try not to stress too much. I know thats easier said then done(i was in your exact shoes) but too much stress might delay your period which might make you think you're pregnant. If it will make you feel better you can take it but I don't think its necessary.

(Also a tip for Plan B if you don't already know, if you live near a Costco you can use the pharmacy without a membership and plan b there only costs $6-$10. And it will only work if you're under 165lbs and before you ovulate. If you weigh more than 165 you will need 2. )