New due date after Ultrasound...?

That is VERY common. They usually stick with the original due date, because ultrasounds tend to get LESS accurate the further along you are (my ultrasound tech told me that). My little guy was measuring 2 weeks ahead at my last ultrasound around 30 weeks. They should have told you that the measurements can be way off, ultrasounds are a good estimate, but that's all they are! Good luck!