Overall, the set is decent. Some are essentially the same image though, like #2 and #3, and #10 and #11.
#1 I would get rid of the white paper or whatever it is in the top of the photo. Also, I would try cutting some of the top off to emphasize the horizontal composition you seem to be going for.
#2/3 I like #2 better, although you could clip a little off the left of the photo to give the car "somewhere to go" in the frame. And that lamp post in the front of the car is distracting. I like 2 better because the car is a little richer in tone (on my monitor), and the angle is a little less extreme, making the car look less stretched.
#4 I like this one compositionally. Everything points to the car, with one exception: the blue box with the "2" in it. I feel it steals the limelight a little.
#5 Ditch the yellow thing on the left. Other than that, this images feels strong to me. It gives the car movement while it stands still. Only thing that bothers me a little is the uneven surface you shot it on leans it toward the camera. Looking at the pillar in the background I can see the shot is pretty straight. The angle the floor gives the car isn't extreme enough to look like it was on purpose, but isn't subtle enough to be overlooked.
#7 is a little more abstract than the others, and I personally enjoy that. To me it seems slightly on the underexposed side though. Only a little, but enough to leave me wanting just a little bit more punch.
#8 and #9 are very similar as well. I prefer #9 slightly over 8 because it compliments the lines of the vehicle a little better and it offers a little prominence to the raised headlights, a defining characteristic of Porsches.
#10/#11 10 works a little better, but the car is just enough off-kilter to take away from the photograph. The car points slightly down where my eye just wants the bottom to be parallel with the bottom edge of the photo.
I would say that for a first shoot, you did well. There are untold numbers of images of people's cars online, and I find that strong car photos are notoriously difficult to find and pull off. To me, I think you gave the vehicle just enough tone and definition and managed to highlight its glossy finish without picking up too many ambient lights/reflections and without blowing out or underexposing the rest of your image.
Keep shooting, as always.