How do I stop worrying?

Chevelle
I had an ultrasound at 6w5d and everything looked great. It was measuring 6w2d and had a heartbeat of 122bpm. 
I can't stop worrying that there's something wrong and that at my next ultrasound that the baby will have no heartbeat. 
I don't have any cramping or bleeding or any miscarriage symptoms. 
But my symptoms have somewhat decreased over the last week. I'm 8w0d today. 
How can I stop worrying? What are the chances? 
I've had 2 miscarriages with no living children previously and just can't believe that this one could possibly work out. 
Help