Hospital said I wasn’t pregnant 🤔🤔🤔

So I went to the ER due to nausea and constipation. They did urine test for pregnancy and blood work for God knows what. I got my BFP on Oct 28 from 3 different tests. So the nurse gave me fluids and zofran. They came back and said my test results were negative that I wasn’t pregnant. So I went to pick up my zofran and decided to buy another test. Mind you I’m taking this test after 1 liter of fluids. Bam 💥 BFP. Has anyone ever experienced hospitals being wrong? If they did blood work could it possibly be that they didn’t check for pregnancy???