Can you keep the character little more towards center vertically? You can probably then add 1 or 2 more zombies in the bottom-left side of the screen.
The icon border needs to be more wide. It needs to be visible at when downsized to 57 by 57 pixels. And it needs to look when downsized to 72 by 72 pixels. Just make sure the border is wide enough for those resolutions.