I've edited your title because missed abortion suggests you had gone for an abortion which failed and isn't appropriate in this forum (for those wondering there is an abortion support forum).
There really is no answer to this until your doctor confirms either way.
In my personal opinion, and through my research (I am not a medical professional), non viable pregnancies do not continue to produce hcg beyond around 8 weeks.
You don't say how far you are.
I object strongly to doctors who make diagnoses at 6 weeks pregnancy because it is exceptionally difficult to see the absolutely minutely tiny embryo at that point.
if you are less than 8 weeks then it is possible that the pregnancy is not viable, if you are more than 12 weeks and your hcg levels continue to rise (even if slowly) then there is a chance that it is a viable pregnancy.
However, as I said this needs to be confirmed by your doctor.