How scary for you, Littlemy. I really wouldn't worry about the Dr turning off the sound - I agree with G43.
There are threads all over Mumsnet (including one of mine) about pregnancies being blighted by worrying measurements on scans. A large proportion of those babies end up being perfectly fine.
Remember all babies develop differently and different bits can develop in a way and at a pace that's outside the norm but quite normal for that individual baby.
The measuremnets are miniscule and when you take into account human error/the angle of the baby/different machines etc etc it's not surprising that so many frightened parents end up with a healthy baby.
I know this probably isn't any comfort to you and I honestly know how terrifying the unknown and your imagination can be. Thinking of you.
x