Dudate change?

So my last period was March 23 and tested positive on April 24th with a due date of December 27th. I had my dating scan on May 15th and baby girl measured at only 6Weeks when based off from my period of should have measured at 7 weeks 4 days. They changed my due date to January 8 and have been going with that. However, I just had my anatomy scan yesterday and is measuring exactly a week ahead. I was 20weeks 2days and she was measuring 21weeks 2days. Do you think they will change my due date again?