Twenty & Terrified

My boyfriend and I have sex quite a bit. I went out of town for almost a week and when I came back we went at it after a few drinks without a condom and I'm not on BC because I just came off one so I can switch and I have to wait a certain amount of time. He "pulled out" but thinks he may have came a small amount inside of me and now I'm two days late on my period? This happened last Tuesday morning. Should I panic or no?