bf might've finished in me

I've been on birth control for almost a year and my boyfriend thinks he might've finished a little in me but he pulled out before he did and I had to well jerk him off to get him to but he says something was already on my stomach ( we use lube ) and I started my period next week. I take my birth control on time and I always do. Is there a chance I could get pregnant? He's really worried and so am I. I also haven't missed a pill this month so am I safe?