I tried what was posted ealier bout using a temp canvas and such and it still doesn't work, when saving the file it still only uses the original canvas size.
Like i said resizing a canvas only stretches it, doesn't actually resize it at all, so maybe it requires creating a completely new one with the new size entered? Although you cannot set an object size when you create one, you can only create one from an already existing object
Possibly a bug with image manipulator? I set that to the new size too, but when saving a file it always saves as "20x20" which is the original size.