The catch is with any fullscreen scaling the image will still be the size of the screen.
If you use the paster or canvas object you can do this instead:
https://www.dropbox.com/s/mdb3cy5pwt7eb ... .capx?dl=0
1. A snapshot is done
2. The image is loaded into a Sprite that covers the view.
3. That Sprite is pasted to a paster object that is positioned to the spot you want and with the image resolution you want.
4. The paster.imgUrl expression will give a base64 URL just like the canvassnapshot expression to save the result.