For our mm/c our bub also measured 8wks (at 10.5wks) and had no h/b. Once you get past 7wks there should definitely be one and we had seen the h/b at 7wks. Even so, I had the same doubts as you (even with the very, very thorough u/s our OB did), mostly because I didn't want the mm/c to be true. We opted to have genetic testing done after the d&c and I found those results (2 chromosomal issues) helped eliminate those doubts.

I think it's probably very normal to feel that way. At 8wks you should definitely have seen a heartbeat as that starts between 6-7wks.