HCG Results

I just called for my HCG results from yesterday, it was 655. That corresponds with 4-5 weeks pregnant she said. I'm 6 weeks today. So its low, how low I don't know. (anyone have a chart or something of the amount of HCG and # of weeks pregnant?) The real question though is are my numbers doubling. I have another blood draw tomorrow and will get those results Thursday, so some more wait and see.