I would wait 2 weeks and go back for another u/s. at 4 wks, it is WAY too early to pick up anything or even be able to tell what the G-O is... my first u/s was at 6w6d and i measured 2 days ahead at 7w1d, saw everything including a heartbeat. So pls wait and go back in 2 weeks... :-)
Oh and at 5 wks my hcg was 12000.