Ultrasound weight accuracy?

Hey ladies,

I am 39 weeks on Thursday and scheduled for a c section on friday 23rd. Original due date us aug 29th. I have gestational diabetes which means I get growth checks every 3 weeks. Well af 38 weeks my baby Liam was measuring 11lbs. Ultrasound lady said her measurements are usually 8 ounces over. My husband doesn't think ultrasounds are accurate at all and is guessing baby will weight 8 lbs max... what is your experiences?