Anatomy scan

So I have my anatomy scan on December 9th. I’ll be 20 weeks pregnant when I have it done, I’m actually really nervous about it, this is my first child so I don’t really know what to expect at this scan. I’m scared that they will find something wrong, I had a 3D scan at 13 weeks. Do you think if anything was to be wrong with her or her heart it would of shown at my 13 week scan? I’m sorry I’m just super nervous.