two different gender results

I had a blood test at 13 weeks to test for chromosomal abnormalities as well as gender. It came back saying I was having a girl. Fast forward to 20 weeks and two ultrasound techs said it's a BOY. I went for another ultrasound today at 21 weeks and a third technician said boy. The picture definitely looks like a boy! But the blood test is 99% accurate. What do you think?!