should I be worried?

So last night my boyfriend and I were getting pretty into it and we didn't have sex or anything but our parts were rubbing against each other sometimes during our make out session. I don't know if I was just really wet or if it was his precum or both but there was no contraception involved. He didnt ejaculate near me so whenever we were rubbing it was only precum. It never went inside like I said but it was very close. We don't want a child because we're still very young (18). My first thought is to get Plan B this morning because I'm really paranoid and I would like to know if that would be the rational thing to do just to be on the safe side? Please help >.<  (Also, I wasn't ovulating and I'm suppose to be starting my period sometime between today; Monday, and Wednesday).  My last period was from December 21st to the 25th  and I was supposedly ovulating between December 30th and January 5th. my cycle usually lasts between 26-28 days so it's pretty regular.        Thank you for your help in advance ❤️