First of all, make sure your image is 72 dpi (dots per inch) this is a setting in Photoshop under image size.
An LCD monitor of any type can only output 72 DPI, any "extra" pixels are discarded by the monitor and the
resulting image is anyone's guess. I had a similar problem with my F series AVIC system even after resizing,
so what I did was to put the image on a black background. That way, even when it didn't fill the screen, it looked
good.