Don't give up hope yet. If in fact you are miscarrying, there is nothing to stop it...but the fact they are letting it happen naturally will give you the time to find out for sure, so if in 2 weeks nothing has happened ask for another ultrasound. You will know for sure then. I wouldn't have a D&C though just wait and see
I first want to say so sorry that you have to go through this. It can be so confusing and frustrating when you are worrying and it doesn't seem like your provider cares. You HCG numbers are supposed to double every other day so your numbers should have been about 1600. Beings that they are going down it is showing that the level of HCG in your blood is starting to decline which unfortunatly is common with miscarriage. Is the doctor ordering another HCG level for you? I would at least ask for another one just to make sure that for some unknown reason your levels just were wrong that one day and now they are going up again. I would say that if they agree and do another blood test at least you will know for sure. The only thing you can do is wait to see what happens. Again I am sorry that you have to go through all this and I hope everything works out for you. Good luck hun.