Reassurance I guess.

I went to a growth scan today where they told me baby is measuring 5 pounds 5 ounces already and that I need to come back in 3 weeks for a repeat exam and to talk to my OB about my baby's measurements and what it means for birth. I'm 31 weeks 3 days and this is my third baby, I have hypothyroidism, I'm not diabetic and I only weigh 160 pounds (I've actually lost weight this pregnancy). My first was 5 pounds 10 ounces and second was 7 pounds 12 ounces. This baby has been measuring 2 weeks ahead the whole pregnancy and now her belly and head are measuring 33 and 34 weeks, her arms 35 weeks and her legs 36 weeks. They said today they won't be changing my due date even though they acknowledge that they messed up my due date by 2 weeks at my dating scan and said I might have to take the diabetes test again even though I've already taken it twice and both times were really good. I know her legs are really long (my husband and his family are all over 6 feet tall and I'm 5'3) so I'm just hoping that her legs are what's throwing off her weight measurements since her belly is only measuring 33 weeks. I'm just super annoyed and scared that they are wrong about my due date and something could end up happening to my child or I'll have to have a c-section which terrifies me and that they're leaving me with no answers for 3 weeks.