I'm the world's biggest worrier and it's really hard to not think the worst when you go for these scans, but I just wanted to say that although problems with the baby and very unlikely, you must be prepared for the sonographer to find VERY COMMON problems in the scans and they may send you back for another one. This does NOT mean that your baby necessarily has any problems but they are soooo careful to triple check any slight abnormal measurement or something else- please don't let it worry you too much though as I know so many people that had to go back for one reason or another and their baby's were fine! They said my child had a smaller than normal head measurement and I worried myself sick, but it turned out that she just had a petite head and she is a totally normal 18 month old now. I'm just trying to prepare you for this as I presumed we would go away from our first 20 week scan all happy and cheery and we left feeling like the only ones going through it- when later on, we found out lots of friends had to go back for re-scans too and all was fine.
You'll be fine though, and try to enjoy it, as it goes quickly.
xx