What are the chances of pregnancy?

Ok so my girlfriend and i were dry humping for like 10-15 min and i have my briefs on and she had thin sweat pants on kind of like pj's and her underwear on too! im kinda scared just wanna know what are the chances of her getting pregnant? i didn't ejaculate just noticed a drop or 2 of precum on my briefs. after i was urinating after the whole thing. should i be worried?