Nervous

Hi! So, I know that no questions are dumb, but mine does feel a little silly. My boyfriend rubbed his penis against my vagina about twenty minutes after ejaculating (he had cleaned up with paper towels but not washed with soap and water). I am a virgin so I'm not on contraceptives and he didn't penetrate anything, but we both woke up nervous that leftover sperm could've made me pregnant. I know- it sounds so silly, but I'm considering getting Plan B. My period is wildly irregular so no help there. It's been about 48 hours since this happened so I do know that I need to act quickly if I'm going to take Plan B, but I don't want to take it if it isn't necessary and further cuss with my cycle and lower its effectiveness in the future. Any advice?? Opinions?? Help talking me on to or off of the Plan B train? Thank you!