Powerpoint Image size changes when Save as

Hi everyone,

Big thanks to the whole E-Learning Heroes team for opening me to the world of powerpoint as a graphics editor.

I have a major barrier with using powerpoint though - once my graphic is ready to be turned into a standalone PNG file, I right-click and "Save as" .  The image then gets exported with larger dimensions than the original.

Another thread here suggested doing Paste special > PNG to maintain the image size.  Firstly, I need the images exported out of Powerpoint for my course materials.  Second, when I tried Paste special, the problem was all the same.  Image comes out about ~15% larger, losing much sharpness.  (see images attached)

Any ideas?  I've searched online and no answers in the general public.

THANKS!