I’ve resolved this by switching to using Google Forms instead. Not as fancy as appsheet perhaps. But since the “app” is a one-page enquiry form open to the public, Google Forms is a better option than being charged to have my business logo squashed. ...

I think it has to do AppSheet defining a bigger margin on the lateral sides (30px) than the top and bottom (5px). The image then get ‘squoshed’ from the sides. See screenshot.