Hello, and welcome to autemo!

If you could post a small 800px preview of your chops first, that would be great - gives us a little more to look at when we first open the topic

For this you will need the 'Direct Link' to the image - I have edited your post so that you can check and see how it's done
On to the picture:
I can see a lot of good work here, with many of the basics covered - neat, tidy selections, and wheels and a backdrop that match the angle nicely
I can also see that you have tried to make the reflections of the image match, but this can be hard when changing a day time image to a night time image, as things reflect completely differently, however the effect is actually ok this time,
The main piece of advice I'd give to you is:
If you're not using it already, use the pen tool to make selections, feather 0.2 or 0.3 px, this way you get nice neat edges to your selections, without any of the 'jaggies' which can sometimes appear. It's also worth checking that when you save the final jpeg image, the quality is set to the highest it can be
Other than that, keep it up - I hope to see more work from you soon, and enjoy your stay here at autemo