Looks like you've been using alot of free-hand drawing on that car, hence the jagged lines. Would suggest you to do some research, dive deep into the webs and find the texture templates which is layered and grouped. Trust me they are there. What many people do wrong is when starting skinning is just grabbing the simple, flat .jpg or .png templates, and start paining over it. Dont get me wrong, you can do lots of great stuff with those templates, but having the layered .psd file makes it way easier, especially when you are at your level of experience. I'll be putting up some texture templates in .psd file on my personal archive website, though I dont know when.
Coming Soon. If you want, I can notify you when I have them up? Though as I said, dont know when it will be done so might take a while.
Other than that, you will only get better with time! Take any feedback into consideration, maybe you one day you'll be able to join the dev/skinning team? Good luck!