Your car looks okay around the rocks, but it's way to light compared to the dark backdrop. It's good for a second chop, your just missing some minor things here and there. It will all come to you as you carry out more chops.
Other things: Shadow under the front kit looks to light, and shadow under the skirt and rear are really dark. And your missing the shadow under the rear tire. Rear rim shouldnt be that shiny (with the backdrop). The seats showing under the scissor doors should be darker. Almost every thing should be darker now because of the background change. Try dding the rock reflections on the front windshield, between the headlights and anywhere else that you see trees change it to rocks. You need something on the scissor door. Doesn't look right. Needs reflections or a light to dark gradient... something. Also need shadows on the body behind the raised door. If you still don't understand let me know.