Window size

I was wondering what would be the best size for a window. I am writing an App with window size 1300x750. While giving a demo, bottom part of the App was not displayed. I noticed that demo laptop screen size is 1366x766 and Windows dock bar is covering the bottom part of the App. So I was wondering what would be the best size for a window.
In all the windows, the contents of the window - list boxes, tab panels etc are in the center of the window. Is there any way that I let the user maximize the window without moving the contents of the window ?