Congrats on the baby! So, that does seem a bit early for the sac to be gone. It 'starts' to disappear right about this time in pregnancy. In my reading, I don't really think it is too early as many women have reported the same thing. I do understand how you feel though as premature loss of the fetal sac can have bad implications for the pregnancy. If it was a big warning sign, I would think they'd have had you see the doctor right away to discuss. I would consider calling and talking to a nurse about it. Why are you having such frequent ultrasounds, by the way? Are you high risk? Just curious. I didn't see my doctor more than once a month for the first and second trimester.
Anyway, congrats!! Is this your first baby?
Being pregnant and especially for the first time is always an anxious time with hopes it all goes well. It most usually does. Is there any chance you have your weeks off a bit and are actually a week or two further than you thought? I think it should be okay but understand your concern. I would talk to your doctor's office. You are having another ultrasound in 2 weeks? That will be an important one for identifying if there is an issue. And of course, should you have any cramping or bleeding, call your doctor. I have a good feeling all will be well. Let me know what your doctor's office says about it and how it all unfolds.
Having a baby was the biggest life changing thing I've ever done. It is so much of a journey and a fantastic one. But this just starts the cycle of worry we have as moms. :>) I'm here to talk to any time!!