Suzy
No formula for estimating fetal weight has achieved an accuracy which enables us to recommend its
use. It should be noted that errors are reported for one standard deviation only and that even at this
level the accuracy is disappointing.
This is part of the policy statement from The autraliasian society for ultrasound in medicine.

They admit that they can not predict the weight of your unborn baby with any accuracy yet the doctors continue to do them

I'm sure that your baby will be fine