5w5d sonogram

It's been a week of hell. Docs saying they are concerned that this isn't a viable pregnancy as my hcg levels rise but don't double, and haven't for a week now. I begged for a sonogram at 5w5d. They assured me I wouldn't see anything. Well, we did. We only saw a gestational sac though, nothing else. They said it's too early to see anything else. But I know women that have. I go back at 6w3d. Should I be as worries as my ivf doc? They've told me to prepare to miscarry and we would need a miracle.