Good attempt but heres the few constructive critiscms...
To achieve the shaddow correctly, it should be a hard shaddow that follows the shape of the car underneath, the blur makes it look like its above the ground from a distance, If you use your line tool to mark out the shaddow outline then go into with the fill bucket you can achieve a perfect shaddow, Remember to use another layer as you may need to edit the lines slightly and or chance opacity of the shaddow, if your skillfull enough you can create a 2 tone opacity, to create the authentic shaddow look.
It will take a while to get perspective right but once correct it should look perfect, add a small bit of blur or go back into the shaddow with the eraser to give it the final shaddow look like below. If needed for those defined shaddows change the opacity of your guideline and erase some of your guidelines, the idea is the lightest part of the shaddow shouldnt have the guidline line, as the light breaks up the shaddow.
A tad slight dust, the front should be just above the front wheel and going backwards, while the back wheels should kick it a bit further up, as this is where the power is coming from, think of it as the more power, the more dust is picked up the less power the less dust, so hence front wheel shouldnt have too much dust coming from it at all.