I understand completely the worrying because it is so natural to be concerned when you want something so much. The thing I want to say is that you can't really prevent lots of things so tehre is no piint asking "what if" or worrying about what "might" happen becaseu you will go crazy.
If something bad did happen, god forbid, then you would cope because that's what we do. You sound like everything is actually going really well so try to focus on that - not easy I know but I've been there done that and in my pregnancy I tried really hard to focus on the positive so it was an enjoyable expierience rather than a stressful one.