I was exactly the same! When I posted threads about it on here, all the ladies who had already had their scans said lots of reassuring things, and now I'm one of those ladies! I still can't believe I'm out the other side of that scary scan and everything was fine, when I was so convinced that there would be something wrong.
Something my sonographer said to me that really helped calm me down was that they find things wrong with babies so rarely, that it isn't actually cost effective for the NHS to still do 20 week scans. She said the only reason they still do them is because women have grown so accustomed to having them.
The only advice I can offer is don't google anything! I went down the list of anomalies that they look for and googled every single one and it was only after that that I started worrying so much. Ignorance really is bliss!!
Trust me, I really do know how you feel, so if you need to talk about this, feel free to private message me xx