How certain were you of the first day of your last menstrual period? It could be that you were just a few days off. Or it could just be normal variation. In any case, with just 5 days difference, they shouldn't even change your original due date... At this early date the measurements are teeny-tiny and the tech being a few millimeters off could make all the difference. The point is, you're in the right ballpark so I wouldn't worry! Congratulations on your little bean -
Yeah, I know.