Changed due date

If your OB changed your due date, I would go with that. If it’s just the ultrasound tech tho and your OB hasn’t gone over your ultrasound scan yet to confirm any date change, I wouldn’t.

I measured 4-5 days off and ultimately we didn’t change my due date.
Most places don’t change the date unless the measurements are off by 10 days or more

At the 12week scan, thats the "due date" they'll use throughout your pregnancy now. Best to stick with that to avoid confusion

They’re likely both wrong but the 12 weeks scan will be less wrong. Only about 4% to 5% of babies are born on their due date. It’s more of a rough window.

My initial date based on my last period was 10th March, they then moved it back to March 5th at the dating scan.
I had to be induced and little one arrive March 18th. So if they've given you a later date, I'd say thats better because your baby is given more time to come on their own without being pressured into induction.