Could my blood test have been wrong?

Nikki
So I had AF on 8/29 and I took a urine pregnancy test on 9/20 (6 days before my missed period) [picture] it definitely looked positive to me. Then today, 9/21, I went and got a blood test that came back negative for pregnancy. Yesterday and today, I started spotting very lightly and it's very brownish pink in color. Definitely not normal for me and my periods are always normal. AF is due 9/26. Could my blood test have been a false negative??