Low heartbeat

I need a little support.  My periods have been irregular, so our best guess is I was around 7-8 weeks.  We had a dating scan today and the dr. found a heartbeat, but it was low at only 104 bpm.  He estimated that I am 6 weeks.  I'm supposed to go back next week for a follow up scan.  I've had two miscarriages and can't help but think it's happening again.  I read a Harvard study that  put the rate of fetal demise for slow heart rates at 6-7 weeks at 60%.  The odds are not in my favor.  Trying to stay positive but feeling pretty low.