the condom came off

Hey, you all! So I need to express something and I need some input: I've become sexually active with my boyfriend and we were having sex one night and the condom slipped off in my vagina. He told me when it happened and I got it out, but I'm still worried I'm pregnant. He says he didn't come and there was nothing in the condom gen it came off. But even still my period is now 2 days late. I took a pregnancy test which came out negative but I'm still worried as hell! Can anyone offer advice?
SOS!
HP