Changing due date in the 3rd trimester?

I went in for a growth scan at 28 weeks and they told me I was 31 weeks. Estimated due date based on their ultrasound is April 10th when it was originally Aril 29th.

Has anyone else experienced this & did they change your due date because you had a big baby?

*The only reason I’m considered is bc my last period before getting pregnant was a miscarriage. It doesn’t make sense that he would have an earlier due date considering I was literally miscarrying our 1st baby (5 weeks) during the time frame of when the doctors are saying he was conceived.*