Constitutionally small? 20wks

I have been a complete wreak today. My midwife sent me an alert/message over my patient portal basically saying she reviewed my anatomy scan and babies weight, skull, and overall bone size is between the 6th and 7th percentile. This makes baby Constitutionally small or SGA. I have to have a follow up ultrasound in 4wks to check If baby is "growing adequately". Anyone ever dealt with this and have any insight? Being in nursing school I know this isnt good to be under that 10% but idk what all it means or why you shouldn't be there. I want to protect my baby and I cant do anything but wait 4wks to see if baby bug is ok or not. 😭