Baby under size?

Aleysha
Anyone had a baby measure under size? I am 31wks and just had my midwife app and she has shown me baby is only the size of a 28wk and 2wks ago she was only 26wks😢 She has booked me in for a scan but I'm just wanting to know if anyone has had same experience. Should I be worried? Do I try to eat more? Is it because I could just have a small baby? Freaking myself out😢