R.K.
The baby most likely was sleeping. We had several ultrasounds to monitor a complication. Sometimes the baby was moving around and sometimes he was resting. Newborns sleep a lot and so do fetuses! He/she didn't know you were watching and that he/she needed to be moving around!
The other poster was right about the way pregnancy weeks are calculated. Strange and I don't know why they measure it that way, but sounds like you are right on target.