Dissappointed

I bought the Limited Edition version of Forza 5 and I downloaded it and everything was fine until I went to buy cars and I purchased the FM5 Mclaren P1 and it came into my garage as a blacked out jetta that was terribly slow. Now it is saying I have to pay 810,000 credits for the P1 when it should be free since I never received it in the first place. This happened to me with the aston martin as well. This has also happened to a couple other people that I know. I am really looking for a solution to get my P1 and aston martin. This is really ridiculous.

That sounds like an issue with the installation. Try the following troubleshooting steps:
http://forums.forza.net/turn10_postsm67044_Forza-Motorsport-5---Game-FAQ.aspx#post_67044

As was said before, sounds as if the install may not have downloaded correctly, or my be corrupt. Try the above process.

Jetta? That’s not even in the game, I’d take it over a P1 any day.