soooo, I'm starting to get really scared...?

Well like a month ago I was at a party. I was completely hammered. I could barely walk it was that bad. When I got home my brother in law called me and asked if I wanted to smoke. (I'm 17, he's 23) I said sure, why not. Like half an hour after we smoked I couldn't even function. I was just sitting there like a vegetable. The next thing I know we're in my bed naked, and yeah. I know he pulled out, but then he put it back in. I only remember parts of it. But I wish it never happened. I regret it so much. I never really thought about it. Then I realized my period was 3 days late. So now I'm really freaking out. I'm scared I might be pregnant and I have no idea what to do. I know I'm going to get judged for what I did. Do I wish I could take it back? Absolutely. What are the chances I could be pregnant? What should I do if I am? What would you do if you were in this situation? Any advice at all?! Thanks in advance.