Grake, I had a blighted ovum last year. I know the pain you are feeling. My ob waited a week to do another scan just in case me dates were wrong and the embryo was too small to be seen. A week later the fetal pole wasn't visable anymore either so I knew it was time for a D &C. Mine was picked up at 8 1/2 weeks after some very light spotting that went away on the same day. The D&C was done at 10 weeks.
It is up to you if you wait and have another ultrasound. It is possible perhaps that the baby is too small as I have heard other storis where the following scan showed a happy healthy baby. The hormone tests will test to see if your levels are rising or falling.
Best wishes hun, the torment of waiting and not knowing is just awful, take care.