Low HCG levels, freaking out.

So I just found out yesterday at the doctors that im pregnant. Im not due for AF until Tuesday. I got blood work done to see how far along i am and i got a call saying they expect my levels to be at 500... im at 63. Do for more blood work next week and im so nervous, if the numbers decrease that it's going to be a miscarriage. Should I be freaking out? But keep in mind im still early and not due for AF for another 6 days, is this what's causing my low levels or is it a miscarriage?