Hcg levels

So my hcg levels are a 695 right now and the doctors at the emergency room thinks I may be having a miscarriage since im like 5 weeks pregnant. They did an ultra sound and at first the doctor was like i see a sac and then the next doctor came in and said she saw nothing. So, my question to you ladies is are they really that low to the point where i can be having a miscarriage?