Why my GUI scale is not working?

Hi!;) I've been googling this for a while but can't get it to work.

I have an option to set my game in Fullscreen mode, the problem is that when I do that the GUI items (GUI TExts and GUI Textures) are anchored right, but the scale is the original.

What I was doing is to call this...

 Vector2resizeRatio = newVector2((float)Screen.width / screenWidth, (float)Screen.height / screenHeight);
 GUI.matrix = Matrix4x4.TRS(Vector3.zero, Quaternion.identity, newVector3(resizeRatio.x, resizeRatio.y, 1.0f));
 
 //screenWidth and screenHeight is the original screen with I designed the GUI

... when I change the resolution by Screen.SetResolution (Screen.currentResolution.width, Screen.currentResolution.height, true); but nothing happens.

Any idea?

Thanks!