Could she be pregnant?

Ok so Im 18 and so is the girl and we had sex and it shouldn't of happened but we did and she takes birth control everyday at the exact same time. And i didn't wear a condom and i pulled out. what are the chances she could get prego. I know they arent high but its got me a lil worried. please answer. thank you! and please let me know if you'd be worried also in the same situation or if i should even worry at all.