Positive ClearBlue Digital - Negative urine test at doctor!

I just took a CBD this morning and came back positive. I’m 4 days before my missed period but I had an ectopic last year so I went to the woman’s triage today and the urine test came back negative. The blood test came back at 22 hcg. I thought CBD had a 25 sensitivity.

I’m so confused - anybody had this happen?