Low hcg and no gestational sac

C
I went to the doctor on Tuesday for an early scan and he couldn't see anything, no gestational sac, nothing. He ordered blood work which came back as 547, and said there's a 50/50 chance I miscarried, or I may just have miscalculated the dates. I'm 100% sure I did not, I was at least 5w5d. 
I had more blood work yesterday and today the nurse called and said my levels doubled so everything seems fine. But that means they are still only 1,100 at 6 weeks.
Everything I read says this is veeeery low.
Has anyone had low levels and no gestational sac at this point and everything turned out ok??
I should add that I got my first positive on a home Urin test 15 days ago (14 dpo), so I assume my levels should be way higher by now??
I'm just really confused and don't have a good feeling. Now I have to wait 2 weeks for another ultrasound and blood test, the wait is killing me!

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