Depo pregnancy

Went to the doctor today for my sonogram scan because I found out I was pregnant 3 weeks ago. My levels said I was about 6-8 weeks pregnant. Today scan showed 2 sacs both measuring 8 weeks but 1 was empty and the other had a small spot in it measuring 3.3 millimeters. What does this mean ? They want me to come back in 9 days to do another scan to see if anything has grown. What are my chances, if nothing is viable what happens afterwards ? Any answers help