This tutorial should be a good read.
Generally, crop isn't the preferred method.
Mmm. The thing is I designed the entire game to work with the crop, meaning that the character sprite is actually too small and the worlds too big to work with scaling.
Anyway for layers you have the system action "Set layer scale" which is basically what you're asking.
I see this is not an AUTO % setting.
This UI should only appear on mobile devices. Is there a way to check the actual current resolution of the screen to properly set the resize?