Scared

I had my first appointment today and I should be measuring 6 weeks and when they did the US she said I am only showing almost 4 weeks. My paperwork for the blood work says "THREATENED ABORTION". I have to go back to do a second set of blood work in a few days to see if my levels are changing. I'm so worried...I've wanted this for years and I've finally got it and now I'm afraid it's going to be taken away from me.