Just hopping over from August mummies to try put your mind at rest Michelle, I've measured small from 28 weeks , Infact bump has only grown 3cm since 25weeks ( 28cm at 32weeks now ) putting my little lady on the 5th centile, I had an emergency scan and she is perfect! Growing as she should, breech and back to back so bump appears smaller, she's at the 20th centile so not a huge baby but within normal ranges.
Midwife told me they have to send for scans just to confirm all well, but tape measurements aren't very accurate sizing wise.
I know it's worrying , I was the same!! But hopefully that helps a little bit....
Everyone is different just my story so far, I have everything crossed for u that your baby is ok, and just tucked away nicely good luck ! Xx