The scans are often wrong but more importantly you don't have GD like you said, your body is making your baby and there is no reason to think you can't have this baby

My first was 4kg on the dot and Asynciltic (wonky and hard to push out (similar to posterior) I had her all on my own
My second who is a beautiful big bouncing boy is 7 weeks old and was 4.81kg, again no intervention necessary and it was definitely an easier birth than my first
No matter what size your baby you can give birth if thats what you want don't let anyone take the chance away on an inaccurate test.

Take all the positive stories hear as your sheild and don't let your doctors scare you into an elective C-section unless that is what you want.

My friend had her baby 2 days after me, they guessed (with ultrasound) that he would be 4.6kg and he was 3.7kg. Wildly off.

Also I have been present for a number of births and there is something about big babies...they are often easier births. In my mothers group the person with the most horror birth story was the woman who had a 6lb bub.

You can do it!
You really can!
And there will be help IF you need it!
And...my big beautiful boy is such an easy baby...many people have told me big babies are often easy... so embrace the idea of a big healthy bub! sounds great to me!