Feeling confused

Just went in for my first ultrasound. Supposed to be 8 weeks today. First day of last period was 7/31. They said the sac is measuring 6 weeks 1 day and the yoke is 5 weeks 6 days, might not be the most accurate as I was dissociating as they were giving me this info. No embryo found so no heart beat. scheduled another ultrasound for 11 days from today. Should I be worried? Should I be preparing myself for loss? Is there a possibility that an embryo could be there in 11 days? Have not been having many symptoms. Just sore and big breasts and frequent urination.