Thought I was 8 weeks pregnant but doctors saying 6 weeks and have been having significant spotting.

Help and thoughts would be so grateful. I started spotting yesterday. At first it was brown, then it was light pink, then brown again, and then bright red. Obviously terrified and super upset. Went to the ED. The take my blood and see your HCG levels are in the 5000's. At the time I believed I was 8 weeks and 1 day because my first day of my last period was April 23rd. They did an ultrasound. Said I was around 6 weeks and did not see a heartbeat. They also seemed not to be concerned with the blood I showed them. I took pictures. I was supposed to have my first ultra sound this coming Tuesday and then my first doctor visit this Friday. They want to cancel my ultra sound and move it out two weeks when I'm 8 weeks. Anyone have any thoughts?? I'm freaking out.