Cubik Studio

Did I do something wrong? Please tell me I can fix this and don't have to redo it... (enlarge the picture to see)

You haven't done anything wrong, this is an issue with minecrafts UV mapping and the atlas system conflicting, causing some texture "leak".
I had this same issue on this model here.

To fix this issue I had to create new 4 new textures of solid colors and then select each element and set it to that specific color.

With this done it greatly reduces the texture leaking.


After this i started making palettes and I haven't had any issues since then.

Palette system should not have such issue.
For the Atlas system, it should be fixed with the setting in model properties to avoid bleeding textures.