No matter how fast a baby grows compared to average or how large the baby is at a later ultrasound, the ultrasound that matters for trying to guess when conception was is the one in the 6th or 7th week, not later ones. The
due date they told you in your sixth
week and in your seventh
week should remain the baby's due date no matter how fast she grows. Some babies grow faster or slower than average. That doesn't change their due date.