Babies are asleep 80% of the time of the day. So there are more chances of the baby being asleep rather than awake at any given point of time, hence the baby wouldn't have moved. Since an anomaly scan requires that the baby be visualised from the front too ( for proper evaluation of the baby's heart), the radiologist asked you to come back. Next time try getting the scan done immediately after a meal. When the baby gets sudden rush of energy from the food you eat, it might awaken and start moving! Don't worry if the radiologist says everything else is fine.