I had the same feelings you are having right now at that stage of my pregnancy.
Stay off your feet, dont lift things, cutting out caffeine can also reduce risk ( i cut out caffeine out of my diet when i was pregnant ) things like that, and of course getting to your doc ASAP, can all help reduce the chance. Miscarriage isnt ALWAYS a defect in the fetus. The mother can do things to cause a miscarriage ... so just take it easy, and dont stress, because that also can make problems.Believe it or not, even when you get passed the stage where miscarriage is more likely, you never stop worrying about your baby.
So try and relax and ENJOY your 9 months!