Cara,
Almost all of us has had this feeling. I was the same as you. I spent more time thinking about the fact that I might loose the baby than I did that I would keep it. The silly part is there is nothing you can do cause this is all in Gods hands. In fact worrying about it and obsessing like you are is likely to have a negative affect on your bub. So as everyone says, easier said than done. Try sending your time researching the positive things you have to look forward to rather than the negative. In just 3 weeks you will already be 12 weeks along and the risk of m/c is reduced significantly. Also remember that bubs can feel your negative attitude and can make him/her feel bad. So maybe start talking to your tummy and speaking positive words. Speaking out positive words is far healthier than quietly obessessing about negative things.
A wise person once told me the 95% of all the things we worry about will never come to pass!