Heartbeat found but still a miscarriage?

Friday we went in for an ultrasound. Baby measured six weeks instead of 7. With a heartbeat of 97. Midwife said its fine as I could have ovulated a week later than I thought. She told me everything looked good.

Wednesday I get my blood test results and they haven't doubled from 61000, have only risen to 81000 in 6 days.

So they get me in that day for a scan. The fetus looked slightly bigger, but they said they didn't know if the heartbeat was mine or the babies at 95... my heartbeat was NOT at 95.... Doctor said it's a miscarriage and gave me all my options.

I'm so confused. No bleeding, no spotting.. heartbeat. Just measuring a week behind. Diagnosed as miscarriage.