Hcg levels at 4 weeks ?

I started spotting yesterday and long story short it scared the shit outta me. I went to the er. And they did a bunch of tests. My levels were only 155 which isn't the lowest they said but they also said in a week my levels should be above 1000. So I wanted to know if you knew your levels at 4 or 5 weeks and if you could tell me basically to comfort me. I am really scared I'll have a miscarriage.