Two sacks one baby with a heart beat. The other sack empty

I had my first ultrasound today. I started spotting as soon as I got there. It wasn’t heavy but dark red. The ultrasound revealed two sacks. One with a baby and heart beat of 138. The second was empty. I’m a little over 7 weeks according to this app. I measured at 6wks 3days. I was told to wait for the full report for a more accurate fetal date. Has anyone had two sacks with one heartbeat and the other sack developed a baby and heartbeat at a later date? I’m still spotting too. There’s no pain or clots. I want to believe the bleeding is normal and the second will develop. But I also want to be realistic. Someone tell me your experience please!!!