Updating horizSizing

Currently I have a GuiTextCtrl with the option enabled so it resizes itself based on what text is inputted using the setText method. I have set the horizSizing of this control to Center, which works fine but when I set the text to something shorter, it doesn't move itself back to the center of the screen - so I was wondering if there was some command to force it to do this or will I have to calculate where it should go based on the resolution?

Thanks.