Anxiety and empty sac 6 weeks

I went to the ER last Saturday due to pain in my right side and Down my right thigh, the on call dr wanted to be sure I wasn't having an ectopic. They couldn't see much on the ultrasound so they asked me to come back in 48hrs to ensure my levels were doubling. I went back in Monday and had my blood drawn again and another ultrasound. My gestational sac had grown and the tech thought she could kind of see a fetel pole but thought it was still too early but said it was definitely not ectopic. My levels had doubled and looked good. My lmp was sept 18th however I know I couldn't of gotten pregnant till October 6th or after due to tracking, when I had intercourse and ovulation testing. The dr said I have to come back in 10 days bc she was still concerned about a possible blighted ovum since I should of been 6 weeks based off my lmp which would of allowed them to see more than they did since then I have been having severe anxiety attacks everyday because now I'm concerned the baby is not growing.  Has anyone had them base it off lmp but the dating not actually be correct?