Ya better mate.
As the others told you before. nothing to add.
Problem with the bg is strange, but I think it has something to do with the
car-shadow too...

Car shadow is indeed too sharp.

Background is currently the worst part in this. Perspective doesn't match at all with the car. The perspective mismatch makes it look like the right rear tire is located "inside" the ground and both front wheels are up in the air (but the shadow is obviously attached to them). Also compare the size of the parking squares. The car wouldn't fit in them. And the body kit isn't that wide either.

I don't think the rear lights would reflect onto the ceiling like that anyway. It would look better without the reflections on the ceiling.

The reason the mustang is sitting weird is that because the car is pointing very far away perspective wise, but the background perspective isnt matching and horitontal line is much too low (View high res image)

http://img905.imageshack.us/img905/2839/UvSfeT.jpg

If you are not sure what you are looking at, have a read here, it'll give you a good understanding
http://architecturerevived.blogspot.com.au/2013/07/how-to-find-vanishing-points-in.html