Hello! I don't think you can upload HD skins on PMC, or Minecraft. The skin you want to upload is 128x128, and Minecraft Java only supports 64x64 skins. I think Minecraft Bedrock supports 128x128, but I'm not sure.

There is sort of a way to use these skins in game. If you install the mod More Player Models, you can use the URL function to get HD skins (skins that are larger than 64x64). Here's a short tutorial from Youtube on how to get HD skins. If that tutorial doesn't help then you can find more by simply searching "how to get HD skins in Minecraft."

However, most textures larger than the default size can be used in game by using texture packs. For example, you could replace the default Steve texture with your skin, which would make all Steves would look like your skin. Here's an example of a Pug Creeper.

I tried to change my minecraft skin into an HD skin but it said incorrect format or something, so what im wondering is 2 things.
Why do you make these skins even though you cant use them
and how do you make this skins? (cool skin btw)

I was able to load it in PMC skin editor but could not upload it. It said "Only 1x skin modles can be uploaded... for now"

I think PMC does not support HD skins, but you could try open your skin in PMC skin editor and publish the skin from there.