Hi Juliet,
Welcome to BellyBelly and congratulations on your pregnancy!
You were so lucky to get to hear the heartbeat at 6 weeks! And how wonderful that it was nice and strong!
I think I can speak for many women hear about just how anxious we all were in the first few weeks of pregnancy! Whether you have been trying for 1 month or 2 years, if it is something you really want, the last thing you want to happen is a miscarriage.
Like the others have said, the best thing to do is remain positive. If you focus on "what ifs" then you will drive yourself crazy.
I remember being really positive though still nervous at first. I think I just kept telling myself that this was our turn and it is all going to be just fine. So far, I have had no complications (no bleeding etc.) and a tonne of m/s so I am taking it that my baby is a healthy little sausage (though it can be healthy with no m/s at all!).
I wish you all the best for the rest of your pregnancy and I look forward to hearing all about it!!
Take care!