Possible miscarriage ?

hi! This is my second pregnancy. My LMP was 9/25 so according to that I would be 8w1d today. I had an ultrasound today and I’m only measuring 6w1d. They could only see the gestational sac, nothing else. The only day we had sex to where I could have conceived was 10/8, so I know conception happened not too long after that day. I just don’t know what to think. I know things can happen fast but I’m just trying to prepare myself for the what if. I go back in next week for a repeat and dread what I could possible see (or not see). I guess I’m asking others if there’s still time for development? If anyone has experienced anything similar? I just feel like even being 6weeks today I should have seen more then just the gestational sac