early ultrasound can be very discouraging thats why I hate them, Try not to worry, see what they say next week, Good luck dear!
I wouldnt try to worry yourself to much. You could have gotten your dates wrong by 2 weeks. Ultrasounds aren't always accurate anyways. If baby's heart beat looks good for his/her 6 week gestation then the chances are your only 6 weeks pregnant and not 8 weeks.
Worrying yourself can cause more stress to you and baby, and Id say your dates are just wrong...and that you should have a healthy happy pregnancy.
Good Luck!