Vanishing twin, survivor?

Hello! I'm currently 6 weeks and 5 days. I had an ultrasound at 6w3d and I had two sacks, but only one baby. One sack was much larger and contained a baby with heartbeat of 127 bpm 😍. The other smaller sack was empty. What are the chances that either: 1. The second sac was in a position where the Dr couldn't see the baby? 2. It'll grow and show up in the next ultrasound?

I feel silly asking, but I want to hear success stories of women who had an empty sack appear a baby in the next ultrasound! My next appointment is in 2 weeks