Worrying is completely normal. Believe me!
In my first trimester I did an embarrassing 13 HPTs. It seemed to be the only way I could convince myself that everything was still going fine.
Even now that I'm in my second trimester and have seen my baby, perfectly fine and healthy, up on the screen, I worry that something will go wrong. I don't think the worrying ever really stops - I suppose it's all part of being a mum!

I think the best advice is to find ways to deal with the worry. For me, that was asking questions (a lot) on BB, and writing/venting in my blog. And although the worrying doesn't ever go, it gets easier to deal with.

Congratulations - and I wish you a happy, healthy pregnancy