scared out of my mind

Okay, so I know it probably isn't a big deal... but last night I was with my boyfriend and we've never had sex. We were just getting heated. Well I was on top of him just dry humping and he cummed through his shorts and onto my leggings. like a lot. it got through to my thong. I didn't think anything of it but my friends have told me and I read somewhere that you CAN get pregnant through your clothes by doing something like that. Here's my dilemma. I'm 18, I don't want a baby. what do you think my odds are? should i wait and see if I get my period? Should I take plan B? I know I probably sound idiotic, I'm just scared! So please, any help or advice would be GREATLY appreciated! Thanks ladies! xoxo