I am 6 weeks pregnant according to my LMP edd but ultrasound scan shows only 3 weeks. Is it normal?

GOw/ultrasound but.. At this early stage of pregnancy the ultra-sound is very accurate at predicting due date (edc) +/- 5-7 days . However '3 weeks pregnancy' is still too early to tell much so i would recommend another ultrasound in 3 weeks (@ 6 weeks to document fetal heart tones). The edc needs to be confirmed. Congrats! and good luck.