How To Confirm A Miscarriage?

my hcg level is 418 & im 5weeks preg. i've been bleeding & cramping very similar to a period w/ no blood clots for almost 24hrs. i got an ultrasound done yesterday & they told me they can see the sac and that it's in the right place. i'm scheduled to go back to the doc & get my blood tested again to see if my hcg level doubles. i am very anxious though and would like to know if this sounds like a miscarriage or not?