This problem should be easy to solve by intentionally setting your desktop resolution to 800x600 after you're booted up, then using the monitor controls to center the image, and then setting your resolution back to 1360x768.
You might've told us about this to begin with
as it has nothing to do whatsoever with the startup animation using the lower 800x600 resolution. Well, not directly, anyway.
Just remember the startup logo is displayed before Windows has even loaded
the videocard drivers
to display the desktop. The reason this works at all is because during startup, Windows accesses the videocard directly through legacy means and simply asks for an 800x600, 256-color screen (otherwise known as SVGA).
This is a legacy screen mode that's always been supported by videocards since the day of games running under MS-DOS and still is to this day.