Armor textures mess up if imported.

I've been creating a joke-ish mod for a few hours now and I have come to the point where I would like to create armor, and I then made a texture for the armor. As I went to import it, I saw that the texture went out of the box where the texture would be on the GUI of the armor texture's page.

I looked into the texture of a pre-made one made in the GUI itself of mCreator, and found that it had a higher resolution than normal Minecraft, so I changed it. THEN I came across another issue, my armor was somehow off the texture of it, even though it went over an actual MineCraft armor set PERFECTLY. I already knew something was definitely wrong at this point, but I was curious so I proceeded to make my armor fit the pre-made armor texture's dimensions and such. I then tried importing it, and it was still out of the box.

Honestly, this is really annoying because a feature like this really stops people from actually putting effort into their textures. Please tell me that I did something wrong or something, or fix this. Whatever the case is, I want to complete my mod.

Screenshot of what happens: https://imgur.com/a/hhVk7Mh