JP
I miss the show so much
You didn’t actually address the problem, you just added more empty padding around the pony (the padding gets removed when the collab is put together). The pony itself is still less than 800 pixels tall. You have to carefully resize the pony part, or redraw it, so that it is 800 pixels or more. You can remove the padding afterwards.
Your pony is, head-to-hoof, only 700 pixels tall.