Random Gray Line?

There’s this random gray line whenever I make a game icon and I don’t know how to get rid of it; I did the correct size, and still nothing. Does anyone know how to get rid of it?

Screenshot_8

What’s the icon’s aspect ratio? I believe if your icon is not the correct resolution (1:1), Roblox will crop the rest out.

I’m kind of new to this stuff and I don’t know what that means. All I know is the size is 512x512.