Photo Resizing Problems

[Becquerel]

Simple. Im trying to resize an image to 512x512 on several different Websites, and each one comes out with vastly different Resolutions.
Hell I tried using GIMP and Paint.net but both of them come out with 643x512.
Hao2fix?

[Ad Bot]

[dkamm65]

Turn off the setting that maintains the aspect ratio. I'm not sure what it's called in paint.net or gimp.

[mntbrrychch]

on paint.net use the canvas resize option (I think that whats it's called) or whatever that other resizing option is that is under the "resize" one and then set the dimensions as 512x512

edit: it's called canvas size or you could just use regular resize one and uncheck maintain aspect ratio like what dkamm said