Overly worried

How do you mommas stay calm and as stress free as possible in your pregnancy? I've heard & read so many terrible stories about miscarriages, premature birth. I'm 17 weeks & 6 days. So far all is good, just heard my little girls heart beat at my appointment yesterday and go for my big 20 week ultrasound in 2 week. Just so worried about what could go wrong. I don't remember being this scared with my first. I did have an amino with him at the 20 week appointment because they thought he had a chance of down but he was all well & healthy. Can't wait for November to be here and hold my little girl!