You can't directly.
25% is the smallest Numbers will go.
Your best chance to get more on a page is likely to be a two-step process.
First off, change your paper size to a larger format - for example, instead of US Letter, use Tabloid, or A3, both of which are about twice the size. You may also have a printer that supports larger page formats.
You can then scale the page to maximize the printed area.
When scaled correctly, print it to a PDF file. This will create a single-page PDF of your sheet. You can then open the PDF in one of many page- or image-editing apps, scale it to fit your page, and print it from there
So not ideal, but the only thing I could think of off-hand.