Well, I Googled it (bad idea!!!) and wasn't reassured. They said the chance of a m/c drops very very low but you're not out of the woods still. There were several stories where girls said they saw strong heartbeats at 6 or 7 weeks and then at 9 or 12 weeks, they went for another scan or appt and there was no more heartbeat. Something chromosomal that means the baby can't grow past that stage :/ But once you get to 12 weeks the chance drops to 1-2%. However, there were a handful of girls saying they saw strong hb's all the way to 16 weeks but at 18-20 weeks, they went for their gender scan and there was no more hb.
So I guess you can't ever be sure but it still has me paranoid now. But the way I look at it, I'm almost to 12 weeks. I can start making purchases here and there now (nothing major but diapers and essentials) but if something goes wrong, the store I'd buy at (my work, coincidentally) has a 90 day return policy so I could always return it, you know?