Downloaded that bg today actually!

Must say you did a great job removing the bmw. I also agree with the others here regarding the size of the car in the bg. I went back and checked the original bg, and there the car isn't much higher then your chop, but it's a lot wider! This is because of the angle of the chop. In order for this car to fit with the camera perspective it just needs to be bigger to scale to the elements of the bg.
Designwise you have managed to create a really nice streetracer styled car, even though you have played mostly with color and added the IC the car looks a lot more evil. Guessing it has to do with the stripes and stance of the car and so on. Really nice work there

Also nice looking rims, but they are to big and the car is too low which makes it look very fake unfortunantly.
The quality of the chop is decent I would say. The largest issue I can see is that you havn't cut out the car properly. There are still dark lines along the roof and back from the original background. You really need to watch these areas, cause it's details like that which will make or brake your chops as you advance further!
Nice chop in any case

Keep at it!
Cheers!