You need to turn on resize display to size of window in application properties and then using the window control object you can do this:
Start of frame: set window x size to MYWIDTH + Client Width - Window Width
set window y size to MYHEIGHT + Client Height - Window Height
The Client and Window sizes are variables in the Window Control object, and you put those in there to compensate for window borders, title bars and menus.
If your window has no border then you can just resize it to the width you want.