Good luck! It sounds like it could be either way, so prepare for the worst but hope for the best.
If you know for sure that you are at 8 weeks, well, you should have seen more than an empty sac. You should have seen your baby wiggling and twirling around and the heart beating. If there is a possibility that you are not actually at 8 weeks yet, then this would not be true. (Sometimes a woman loses a pregnancy and then immediately gets pregnant again, without a period in between, meaning that what she thinks is her 8th week is really her 4th week.) Talk to your doctor and get another blood draw.