Fetal heart scan

I have a fetal heart scan tomorrow and I'm petrified of what they will find. After my 20 week scan and finding abnormal thickness in the neck, I was told there was a possibility of genetic problems. My 12 week scan for down syndrome come back low risk so im scared that what they find is something even worse for my child's health than down syndrome.

Has anyone had any experience of any of this at all. I'd appreciate as much information as possible as I'm honestly freaking out.