My 12week u/s they weren't able to get some measurements because the bub wasn't in the right position and/or moving around too much. I was there for 90 minutes in the end & was busting for over an hour, but they decided to try again at the 18 week u/s after all of that, so I'm pretty sure its normal for them to not be able to get the perfect measurements and want to do so jic. I hope that it is all okay for you two!