Hi there
I am terrible with shadows... but that does not stop me from making a mess...
I do believe the background is just fine, but the floor is a big distraction and also makes it hard to show shadow.
Now I may be way off base here but the seat looks out of proportion compared to the girl behind.
This type of composition is not easy to do as each subject may have slightly different lighting. Like Ken, and unlike me, I would think light and direction and maybe alter the various inserts, then produce the shadow as he stated. But I would surly replace the floor.
Butch