return appt after initial 20w fetal anatomy ultrasound

Vee
My midwife emailed me after my 20w fetal anatomy Us saying that the ultrasound results of the baby were normal, but they were not able to see some of the vessels around the heart due to the baby's position. They are supposed to be calling me back for a repeat ultrasound in the next 2 weeks. Has anyone had this happen for any reason or this reason specifically? With my other kids, I've never had to go back so I'm really nervous!