It's common for due dates to shift a little when the first ultrasound measurements come in. The LMP is just a rough estimate and many of us don't ovulate exactly two weeks after a period. Babies also grow at slightly different rates, so being a week or two ahead or behind isn't unusual. Your provider will use the scan to give the most accurate due date. Try not to worry too much and go with the new date – your little one will arrive when they're ready.