I didn't have a 3d/4d scan with my DD, but I did regulary with all the scans I had with my DS and it was draped over one of his shoulders in all the later scans from 20wks onwards. I had an emergency c-sec for other reasons but when he came out and it was down around his feet.

With my DD the cord was always shown around her arms/belly, never up near her head, but when she came out the cord was wrapped once around her neck and she wasn't breathing and needed help to start breathing. For about a week prior when I went for my CTG monitoring every now and then when she got really active her heartrate would suddenly drop really low and we now know it was because the cord was being pinched between her neck and my pelvis while she was moving around.
She was perfectly fine while I was in labour though, and the only reason the cord was wrapped around her neck was because she did a 300 degree turn while I was in labour to get into a good anterior position to be born, and she's now 6wks and 5d old and perfect in every way so the cord being around her neck didn't cause any problems.

Just remember to mention your concerns to your OB, at the very least they can order some repeat scans towards the end of the pregnancy to see where the cord is positioned.