This may be the most jankiest racing game I have ever played.

Improvements:

Select a color scheme and stick with it.

Your font choice was difficult to read.

Create your own models in blender, or just use Unity's basic shapes till it feels right. The origin of the car may not be in the center of the car. 

In most cases, using assets you did not create requires a license or attribution or permission.

Start small, and learn stuff and do stuff yourself!