Hi, 6wks there's most likely a tiny gestation sac formed only. Normal abdominal ultrasound might not be able to detect the gestation, a transvaginal scan can do the job. By wk8, the gestation sac should be able to see n by abdominal ultrasound.
Did your doctor schedule another scan in 1-2 weeks’ time? It should be visible by then (along with the heartbeat) if the pregnancy is viable. Hang in there, dear...
Madhu