Has anyone had this happen before?

I went to the clinic and they did a urine pregnancy test, and it came up positive, I mean the doctor read it, so it was definitely positive. She gave me a form to book a dating ultrasound and everything. I went to the hospital today to try and get an ultrasound or to hear the baby to make sure it was okay... and the doctor told me that my blood test was negative for pregnancy. They were very understaffed, and super busy, I was there for 8 hours. But I don’t understand getting a positive pregnancy test with afternoon pee, then getting a negative blood test... and I thought getting false positives were very rare...