I agree w/ chantal21....unless your doc changes your due date, I would just leave it as it is.
If your doctor doesn't want to change it, then I would stick with that. With my pregnancies, my babies measured bigger than normal, but my due date was only changed according to the first trimester u/s (which was my first one) After that, they usually don't move it. 4 days isn't too bad. I remember with my second, he was measuring 9 days ahead which bumped my due date to sept. 30 instead of oct. 9. He was born sept. 6 at 7lbs 2oz, so I am glad they switched it then.