2 sacs, 1 empty at 7w4d. Any chance of viability for empty sac?

Angelina

I had my first US today. It showed 2 sacs. one with a baby measuring 8 weeks exactly (i say 7w4d because I know the exact day I ovulated) with a heart rate of 164. The other slightly smaller sac was empty. Any chance there could still be a twin? I just knew it was twins since I found out I was pregnant and now I dont know. What are your experiences? (good or bad)