All i can think about is my baby the doctor told us she was measuring 28 weeks and im 31 but other…

All i can think about is my baby the doctor told us she was measuring 28 weeks and im 31 but other than that she's fine and that he was gonna monitor her but im scared as hell he just tells me some babies are born smaller than others but that wasn't enough for me now im over here worrying. i keep feeling like she's not getting enough nutrients