Can't stop from worrying

I went to the Er when I was 7 weeks for some spotting they told me it was a "threatened abortion/miscarriage",  I saw my real doctor a few days later for a follow up and she said that the bleeding was very small and that it was most likely from the placenta attaching to the wall of my uterus, she said it was very normal. I had my first appointment on 11/11  and heard the heart beat and saw my baby, but since then I have had this horrible feeling in the pit of my stomach that I might miscarry, this is my first  pregnancy, how do you not worry?!?!?!?