Sometimes body parts are just hard to get a good look at. I wouldn't worry about it. So long as you guys caught a glimpse I'm sure it's there.
hi,,, your doctor could tell you what the results from the ultrasound looked like, more than the person who actually did the ultrasound because someone is supposed to interpret the results, so don;t worry , talk to your doctor if you have any concern but in the mean time don't stress . take care.