sorry your post is a little bit confusing, but did you have an ultrasound at 12 weeks? if so that would be the most accurate edd. You shouldn't go by fundal height, its not accurate enough, so if this is how the docs are calculating then I wouldn't worry.
If YOU know when you DTD and you didn't a week before or after then go by the date corrisponding to that. Don't let them push you around.
They wanted me to have another CS because DS1 had been born (via emerg CS) posterior and 9lb 4oz and DS2 was presenting posterior (apparently they wont turn once engaging) at 36 weeks and was estimated to be over the 9lb mark again, needless to say I didn't cave and went on to have a successful VBAC 9 days early and he weighed 8lb and was born anterior.