I like this wallpaper it is simple, and pleasing to the eye.
It does not feel unfinishied, but the overall piece does not mesh together.

The font does not fit the sketchiness of the background, less boldness might help with that and a change of font/effects of it.

the main character however, is halfway there. If not already there, a bit of texture added could make it way better, but careful not to make it too much otherwise it will mix too much with the background and she won't stand out as much as she does now.

I'm sorry I am not much help, wallpapers are not my forte, and terms for photoshop are still very new to me.
Still, I hope some this helped some.

:]

Look at you, Miss Popular. ;)

Well I'm not sure how you would fix it, but if you're looking for critique I can tell what two things seem to not be meshing.

The first is the actual character. She lacks the fun sketchiness of the background so it feels like she doesn't quite blend in.

The other is the font size and placement. It honestly just seems like overkill and distracts from the overall image.

Maybe there's a way to give the girl a sketchy feel along with the font? Something like that might give it a more finished look.

Personally I'd go for the sketchy look since the background is adorable.

I like it :)
The colors really compliment each other.
And I think you might be confusing unfinished with simple :D There's nothing wrong with a simple wallpaper when it looks good like this!
*hugs and favs