tarpyhargque

Hello, I want to make roblox clothes and I'm trying to make my own template. However, I have a problem. When I use the "Rectangular marquee tool" to select the specific part I want to delete, there were left over pixels. This seems to only happen on the image I want to select delete. When I try to do the same thing to the template, nothing happens. Anybody might be able to know why this happens, and how to fix it?