The best way to print the gradebook is to download the gradebook into Excel. Then you can format the Excel spreadsheet anyway you’d like and print from there.
If you want the gradebook to print on one sheet, click on Page Setup under File, make sure the Page Tab is selected, click on Landscape, then in the Scaling section click Fit to: and make sure it says 1.
The print will be small, depending on workbook and margins you set, but size skip the fit to one page, then click on Sheet Tab. Under print titles, add row $1:$1 to rows to repeat at top and add column $A:$A to repeat at left, that way you will have assignments and student names information repeating on each printed sheet.
Click Print Preview at the right of the screen; make sure all the information you need if visible and Print.