Camera overrides let you rescale the screen for different resolutions and aspect ratios. If you set up a wildcard override, and with the default values, it will scale whatever output you have to fit the screen. Eg. 1024x768 -> 960x640. There are options on how you want to scale, so you can tell it to try to fit width, height and so on.
You aren't doing anything wrong. Have you tried your app on iPhone or other android devices? You'll probably find it already does a lot of what you need - when it doesn't, you'll just need to tweak the overrides to suit.