Hmm this interesting, not sure why you would want to print screen a full window of the MS-DOS window, but that's besides the point. To answer your question my suggestion would be to simply make the window full screen (keeping it in window mode) not using ALT+ENTER to make it a complete full screen.
You can right click on the title bar and adjust the window size properties, ie chaning width to 200, height to 300 and double-click the blue bar to make the size full screen (windowed).