Empty Gestational Sac At 7 Weeks

Hi, according to my LMP, I'm at 7 weeks this week. However when I went for my ultrasound yesterday, it showed empty Gestational Sac. It broke my heart as I was expecting to see and hear heartbeat. Doc ruled out ectopic. My sac was 1cm in diameter and hcg is at 8000. Doc adv me to come back in 2 weeks again. Any advice and stories to share? I'm preparing for the worst.. :(