Check which printer setting you're using:
When you go to File > Print (or press Ctrl & P together), don't just hit OK. Instead, click on Properties. Then look for the the sizing options. (With my Canon printer I have to go via a 'Page Setup' tab but you might see something different). Check that 'normal size' (or something similar) is selected, rather than 'fit to page' (or similar).
If you're
only using Powerpoint to produce printed output (rather than an on-screen presentation) adjust the size of your slides to match that of your paper:
https://blog.udemy.com/powerpoint-slide-dimensions/
(or, far, far better, use a DTP program instead. Powerpoint isn't designed for print output!)