Inevitable miscarriage..

the ER doctor told me I am going to miscarry but I am not having any symptoms of a miscarriage. I am still having pregnancy symptoms such as tender breast, fatigue, nausea, cravings, etc. They said the sac is measuring 6 weeks instead of 9, could I just be earlier than anticipated? Could I have ovulated late? My HCG levels are 43,397. Any comments would be greatly appreciated as this is my first pregnancy. Thank you in advance.

PS - my last period was July 22 and I had my first positive pregnancy test September 2.