Follow the instructions to do a print hack! if somehow the project isn't working i'll explain it in the notes and credits.
first, upload an image into scratch i recommend remixing this and doing that. next change the size until it's the size you want. then right-click the bigger image and click save image as... after that, open google phottos or gallery and select the picture. do Ctrl+P and then it will show you teh image, where its gonna print, and what'll look like. if you like the size press print. congratulations! you did a print hack!