Congrats on the Baby!
If there are no other reasons for the baby to come out then I would not worry about it. Babies are on their own schedule.
My daughter was right on schedule until my last ultrasound at 36 weeks. Her head was only a 32 week and the rest of her did not go past 34 weeks. Then she was born and her head was still small - they say - and now at almost 3 months her head is in the 25% and the rest of her is 50%. She is fine. she can roll and babble and everything she is suppose to do. I would ask for more information about why they think the baby needs to come out. If they think the cord is being crushed or something with how the baby is laying, ask for exercises or alternative to help move the baby around. Good luck!