You are doing right, but just do one thing more to insert a page break. In manual page breaks you have change the scaling option to Adjust to instead of Fit to in Page Setup dialog box.

Follow these steps to do your task:

1.Go on Page Layout section.
2.Now open Page Setup dialog box. You can find this option in Page Layout section, right corner at the bottom.
3.In Page tab of Page Setup dialog box, select Adjust to scaling option instead of Fit to.
4.Now follow your steps to insert a page breaks.