Only can see the sac

I totally understand the worry, this must feel quite stressful. At 6 weeks, timing can be tricky because it really depends on when you actually ovulated, not just your last period, so sometimes things are a bit earlier or later than expected. A few mums I know went in expecting to see more at that scan and only saw the sac initially, but when they went back a week or two later, the fetal pole and heartbeat showed up fine, so it's not always a red flag. That said, some situations do need closer monitoring, so it's definitely worth asking your doctor to recheck in about a week or so and maybe also check your HCG levels to make sure everything's tracking as it should be. Try not to spiral too much in the meantime, but do follow up, your own doctor or specialist will give you the clearest picture of what's happening with your specific pregnancy.