Uhg 4 days behind

Hello! At my 7wk2 day scan my PGT tested FET IVF baby measured 4 days behind (was only 3 days behind at my first scan). He had a great heartbeat. I’m very symptomatic. I think my guy implanted late because his first HCG was terrible but it doubled excellently. My Dr. said she doesn’t like that he’s 4 days behind (I guess with IVF it’s okay to measure +- 3 days but not 4) but also not to “lose sleep over it.” I’m losing sleep over it lol. Any thoughts friends? Thanks!