Ultrasound a week off?

Amethyst

My midwife sent me to the hospital to get an ultrasound because I'm measuring 3 weeks ahead. I went in, have normal fluid levels, and my baby girl is weighing around 7.14-8 lbs

All the ultrasound measurements came back and I'm measuring 37 instead of 36 weeks

I had irregular periods so...is it more likely I'm farther along or the ultrasound is wrong??