Possible miscarriage?

Hi ladies, so I'm really just looking for comfort. I went to the emergency room on Sunday because I started bleeding, it was light. This is my first pregnancy, so I'm really concerned. I was 6 weeks and 5 days. They did an ultrasound, and there was a heartbeat. But they did tell me that I was about a week off, and the baby was measuring at 5weeks 6 days. I know they say that once there's a heartbeat, the chance of miscarriage drops, but now two days later, the bleeding has only become heavier, and now there are small clots. I have an ultrasound scheduled for tomorrow afternoon, but I am just so worried..