Making myself freak out

I know i tend to over think things and then make myself so nervous. But we found out we were pregnant for baby #1 last week the doctor gave me a due date and said i was 7 weeks today. Well i went for my ultrasound a lil while ago and its looking like im only 5 week 6 days today. That seems like such a huge difference! What if my baby isn't growing or something wrong! I cant help but feel so scared amd nervous.