Could I be pregnant?

Perla

So in the 9th of December I started my period, and I had intercourse that same day with my partner and he didn’t pull out he let it all inside of me. And that was the only time we had intercourse and I’m never have been late. I’m 3 days late, did a pregnancy test yesterday and it came out negative. Could I be pregnant or is it a false alarm? 🙈