So about two weeks ago I had an ultrasound at a pregnancy resource center and they said I was measuring just at 6w1d

They were just volunteers. Well I had an ultrasound today at my actual obgyn and the tech said I was measuring 6w6d-7w1d and she couldn’t find the heartbeat. Is it possible I was only 5 weeks at my first ultrasound and that I’m still too early for the heartbeat. My doctor ordered a blood test and said she thinks I’m going to miscarry but I’m trying to be hopeful still. I haven’t had any cramps or bleeding.