Re: I did not receive the event reward

Unless I've misunderstood it sounds like you got the same reward as everyone else. You don't get a fully maxed out car as the reward for the event. You have to spend gold on BPs from the event black market if you want that. Alternatively you can wait for replayable races (likely but not 100% certainty) where you will be able to earn some additional BPs but it is highly unlikely that this will give you anywhere near enough BPs to max out your Lamborghini.

This is just how free to play games work. Although they can be played for free, everything the devs do is designed to encourage you to spend real money.