Due date confusion

Cassandra
So im currently 25wks ACCORDING to my first day if my last period which i alwayd kept track of so there is no mistake there. I see a high risk because I am type 2 diabetic anf because of the babies heart. Well i see the regular OB because thats who is going to deliver me. This will be nu fourth planned Csection so the plan id to have her at 30 wks which according to the last period would be the week before July 7th. My regular OB keeps saying that im due july 17th and he isnt going to deliver me till July 12. I do not agree with this. Would i be wrong if i tell them i want to be delivered the week before my first due date. I heard it dangerous to keep the baby in longer then 39 wks because of the diabetes and their due date is wrong and that would be 41+ wks. Thank you for readig this