Can you get a bfp on a clear blue digital weeks estimator at 3 weeks pregnant?

I found out I was pregnant November 28th and it said 1-2 weeks pregnant. I went and got an ultrasound down today and they dated me as 4w3d and that would have only made me 3 weeks when I got my first positive! I'm wondering if anyone else has gotten a bfp so early on the clear blue digital weeks estimator? Or if it means my hcg is really high? My husband's aunt just had a dream about us having twins, a boy and a girl though. And there was only one sac in our ultrasound so it would have to be identical... but I doubt it hahah neither of us have family history of twins!