keys there is nothing about your situation to suggest that everything isn't fine, honestly. If you are not sure of ovulation and are only 5+4, they definitely wouldn't see a heartbeat. Of you are certain you are 6+5 then it is very possible the measurement is wrong. Apparently the margin of error on these machines is at least 1 mm. Your tiny baby is only about 4 or 5mm and so that margin of error is over a week!
When I was having my mc, I was really annoyed when people said that my dates could be wrong- but that was a 9 week pregnancy measuring 6 which wasn't possible. That would have many I had a positive pregnancy test before I even conceived.
But it isn't false hope with you. It's just so much more likely that everything is fine.