DNC - miscarriage but no blood work!

I have a question- I was told on Tuesday at my first ultrasound appointment I had a missed miscarriage ... they said I was supposed to be 9 weeks but measured at 8 which means I lost it last week. Again this is all based on the ultrasound Bc they found no heartbeat. Now I’m scheduled for a DNC tomorrow and wondering if I’m doing the right thing. My friend who had miscarriages said she got blood work first to confirm pregnancy and then a second time to confirm miscarriage. Why didn’t they do that!? Is this bad practice? Any chance they are wrong and I never had a miscarriage?! I’m debating on if I should cancel my surgery tomorrow now. Anyone else have this experience of being told no heartbeat and that sufficient that it’s a miscarriage?? Just feeling like smthng is wrong here but this was my first pregnancy so I don’t know much either. Please help!