I'm freaking out

Okay so last Wednesday my boyfriend came over and we had sex. (With condom) towards the end he pulled out, took the condom off and decided to finish on my stomach. When he did, some of it rolled off, and landed near my vagina. Since then I've been really scared there could be a chance I could be pregnant. Sunday night I went and bought a pregnancy test and it was negative, but my period is three days late now, and lately I've been feeling really nauseous all the the time and I'm scared. Do you think I might have taken the test too early and I got a false negative? Is there even a chance I could be pregnant ?