Gestational sac measuring 6 wks and egg measure 4 wks? no heartbeat but if i'm 4 wks, i was told they wouldn't be able to hear it. will i miscarry?

Clarify findings: I am not sure what you mean by the measurement of the egg or what exactly was measuring 4 weeks. With a 6 week size sac the doctor will be looking for a fetal pole and trying to find a the fetal heart rate. I would contact the doctor and ask for clarification of what was found on the sonogram and ask for a follow up plan. Typically the sonogram would be repeated in about a week.