possibly pregnant

Me and my boyfriend were having sex and when we do, he doesn't wear a condom, which we should, but he pulls out. But anyways, we did it and he pulled out and everything was fine and then we did it again, without him pissing, so there's a possibility that his precum had sperm in it and then to top that off, he was about to finish but just stopped in me until he felt like he didn't have to anymore and then pulled out. How big of a chance do you think there is that I could be pregnant? Any advice would be helpful.