Week behind?

Supposed to be 9 weeks tomorrow but at my ultrasound Thursday ( I was 8 weeks 4 days) baby was measuring between 7 weeks 3 days and 7 weeks 5 days.

Tech did abdominal ultrasound and she made a comment about letting my bladder fill up more, which I don’t think it did.

Could the measurements have been off? Baby had a heart rate between 150 and 170. The only reason I know is because I saw the screen, she didn’t tell me.

Is this normal to measure a week behind at this point?

Thanks!