The CRL only measurers the length of your baby not its size. In fact the Australasian Society for Ultrasound in Medicine in their policy 'Statement On Normal Ultrasonic Fetal Measurements' state the following "No formula for estimating fetal weight has achieved an accuracy which enables us to recommend its use."
There are a number of posts from women saying how inaccurate the US was when predicting the birth weight of their baby