Plan b needed or no?

okay someone PLEASE help me out here.  I've been in a situation like this and I ALWAYS scared myself into buying plan b which obviously gets pricey. Tuesday I had someone over and it wasn't even really sex. there was no penetratation and I didn't realize this but I was supposed to start my period yesterday and it's late by just a day. I'm really just wondering if I should take plan b just to be on the safe side or to wait wait for my period. tomorrow will be the 3 day window for plan b I've just been waiting to see if I get my period