I'm sorry if the wallpaper doesn't fill up your whole computer screen. It is dissapointing but I dont't have the thing for different size screens. Just the wallpaper you see. I tried making the wallpaper bigger to fill it up, but it makes 0% difference what size it is before you make it the background.

 

But I now have a solution to this. Save the wallpaper image by right clicking it and hit "Save picture as..." Then open the folder or whatever it's in or if it's on your desktop or whatever. Make sure it's in thumbnail view, and don't open the image. Now right click on the saved image and select: "Set as Desktop Background". And there you go. If you have trouble with these directions let me know and I'll help you. ^^