Crosshairs Gui don't stay the same how to fix???

When I maximize my game the crosshairs don't move to the middle of the screen like they were before the game was maximized, they just stay over in the corner, how do I fix this?

Put your center-finding script in Update, like this:

var button = Rect (0,0,20,10);

function Update() {
    var center = Rect(Screen.width/2 - button.width/2, Screen.height/2 - button.height/2, button.width, button.height);
}