Secondary u/s tomorrow.

This is the first u/s I am more nervous than excited for. I went in for my anatomy/gender scan at 18 weeks. A few days after, I got a call from my doc office saying they needed to schedule me for another u/s but wouldnt tell me why. I have an appointment with my doc in the morning, and the u/s in the afternoon, so I will get to talk to him and see whats going on then. I am pretty sure they just need some more/better pictures of the anatomy, because she seemed to have a hard time getting them. She even commented on how she didnt know why they schedule them that early because it is hard to get the pictures. Anyways, I'm really hoping thats all it is, but of course I still cant help be nervous. So any encouragement, or similar storys are much apreciated   TIA

I had to also have a second ultrasound at 22 weeks since they couldn't get good pictures of his heart at 18 weeks so i'm sure thats all it is.