I've tried many things since yesterday.
Finally, i've set the Scissor to (0,0,639,479) and let the DisplayAspect to -1.
All is ok on Windows, Android, Ipad, but there is still this problem on RPi 3.
When i maximize the window OR when i set my game to Fullscreen, it doesnt fit the screen.
There is also an other problem.
AGK thinks the game fit the screen, so sprites positions and UVs are not drawn where it should.
Even when the Window is not maximized.
I've also tried an other TV with better resolutions, same problem.
I think there is a bug in this for the RPI's AppGameKit 2.
My Freewares here : http://www.retro-bruno.com