Why do I still fear miscarriage?

I’m 17w2d and still fear of a miscarriage. This is my first and I’ve always over worried things. I went for my ultrasound last week and he’s a baby boy moving around and they say he looks great. He’s even measuring 5 days ahead lol. I just can’t shake the feeling though. I feel like if I get too excited I will jinx it. Anytime I get cramps or pains I instantly get scared. When did you start to get excited?