What due date to go buy?

So today I went to my Dr he say that he’s going off of my 5-6 weeks scan. Only probably was he was having a hard time viewing anything because the position of my uterus, so he sent me out to a specialist. They couldn’t see me until I was 13 weeks which by then I was measuring 14 weeks and a few days on that ultrasound. They sent him a change of due date but he never changed that. They gave me a new due date of 11/26/17 but off of his ultrasound machine which he couldn’t see much that’s why he sent me out in the first place, he has me at 12/3/17. With that being said I’ve been diagnosed with gestational diabetes and having a c section so won’t that put me at 40 weeks delivering c section? Aye I don’t want to go that far.