If the baby isn't in the right position any picture isn't going to give you the right information. To get accurate measurements they have to be in the right position for the sound waves that the us uses to be accurate. I deal with u/s and measurements for hearts and their valves etc on animals weekly, its part of my job and I know that you have to have everything in the right place to be able to get accurate measurements.

If you are concerned, speak with your hospital or your GP. The measurements need to be done between 11.5-13 weeks.