My baby boy is big

Cierra • This mine and my husband`s third child. We have a handsome boy and a perfect little girl. We are expecting another boy and couldn`t be happier
I went to the doctor yesterday and I am measuring 27cm and I am only 24 weeks, my doctor scheduled a sonogram for my next appointment to see why he is so big. This is my third pregnancy and never go t told that. Should I be worried??