Confused?

Su

So, according to my first due date(Dec21st) I was supposedly 20 weeks, but when I went to my anatomy scan my baby was measuring ahead at 21 weeks 3 days, and the ultrasound tech said the Due date for those measurements was Dec 12th?

So, am I actually 21 weeks pregnant or is my baby just measuring big at this point? Is my due date the same or did it change!? Y’all, I’m so confused 🥴