Insert page > Blank page > why not A4 size??

After scanning a 70 year old page, and then editing it, I thought my blank pages where coming in as A4? as when I finish editing and come to export / print it's made the page size the same as the old page so I have large blank areas at the top and bottom. I will have to do all the 10 pages again !

Why am I not working on A4 ??