Any test on blood and urine needs the lab to be looking for something specific, so if you had a urine test or blood test last week they may have just been looking for other things (there is a set of prenatal screening work that gets done to see if you have antibodies to certain diseases, see if there's sugar in the urine, etc.). So those tests don't mean anything within the context of your question today.
I would not have a D&C without being assured that sufficient evidence could be produced that the fetus is not living. There is a blood test that can be done that is more accurate than pregnancy tests on urine.
It is possible for the embryo/fetus to stop developing and not be expelled right away. Look up "missed abortion" or "missed miscarriage" for an explanation. It is possible to go on for a while and have a placenta but to have no fetus in there because it stopped developing/living. In a situation like this the pregnancy hormones will eventually return to a non-pregnancy situation; but it can take a little while.
So many pregnancies end early (something like one in ten) because of a "blighted ovum" (there is just something wrong right from the beginning and normal development doesn't progress), and if a fetus dies it may take a couple of weeks before it is expelled (and, as I said, in the case of a "missed abortion" it may take so long that it has to be cleared out by the doctor).
Having no spotting or cramping doesn't necessarily mean anything. These days the ultrasound equipment is so good I would think you should be able to request to see the images and have the doctor/nurse explain to you what they don't see if there is still no heartbeat to be detected. That may satisfy your need to know for sure the fetus has no heartbeat.
If, in fact, there is no heartbeat there is a good chance that what is wrong with the fetus is nothing more than that something wasn't quite right from the beginning. Early miscarriages or fetal deaths are not necessarily associated with anything more than that, like genetic problems or problems with the mother. Its possible the fetus could have stopped developing a week or so ago, which would bring you back to 7 weeks along (a high-risk time).
If the baby "measures" to six weeks it would seem to indicate that it could have stopped developing at that time. Human fetus development is pretty uniform in the beginning.
Write down every question you have and sit down with the doctor and ask her to address each of your questions.
I know what you're going through. I went through a similiar version of events, only a little later. The most difficult thing is to find a way to be certain that there is no mistake being made by the doctor. I actually asked what would happen if I didn't have the pregnancy taken "just in case". The answer to that was that I would become very sick, and waiting too long was not an option.
Use this week to prepare for the worst, and if the worst doesn't happen then great.