So scared! Possible abnormal anatomy scan

I had my anatomy scan a couple weeks ago at 19 weeks and at the time everything seemed great! Found out we were having a baby girl and she was very active! I had a routine check up appointment today with my regular ob, listened to the heart heartbeat and it sounded good at 137 bpm. When I asked her about the results she claimed everything was okay, but said she wanted to set up a repeat ultrasound to take another look at my baby's brain. Her explanation was that they simply "didn't get a good look at it" last time. They set up my repeat ultrasound for a whole month from now! I am a first time mom and officially FREAKING OUT!!! Has anyone else had this happen to them? Is it possible they really just didn't get a good angle and that everything is okay? I am so terrified and just really need some reassurance right now.