I wanted to pass along a great link (below) from WebMD that helped me out when I was in the same situation......
Not knowing what your LMP is but looking at your post you are concerned about whether they are correct in assuming you have had a mc. I also had the same thing happen and was sent for US. They found an intrauterine pregnancy, however, at 5 weeks 2 days it was too early for them to find even the fetal pole let alone a heart beat. I was sent back in for follow up US at 6 weeks 3 days and they found everything where is should be and the crown rump length measured just one day different than my own dates.
All I can say is if you are not convinced....demand they do another US between 6 - 7 weeks from LMP.
This link will explain everything about early ultrasounds and even early quantitative HCG testing....
I am wishing you all the best....
https://blogs.webmd.com/healthy-pregnancy/2005/11/hcg-levels-and-ultrasounds-in-early_30.html
Re: melodylb - RE: Post about Ultrasound prior to D&C