print dimensions different from file dimension

Hi, I have used InDesign over the years but have never had this issue so I was hoping someone could help me out. I set the dimensions of my file to 20w x 7.5h but when I print the document, it's roughly 26cm long and 10cm high. I have double checked the size in document setup and remade the document to see if that changed anything but it hasn't. I'm sure there is just a setting I need to change but aren't sure what that is.  Does anyone know how to fix this?