I would use some soft colors in the Blues, Yellows, and Pale Reds for borders. Maybe one of each--2" wide each. Then a binding of again one of the colors in the quilt, but again the darker shade--dark Blue.
I think that will tone it down some, but yet, I think people will expect bright colors with a car quilt.
I personally think it is great!
We get too hard on ourselves when we look at our own work, is my opinion. I finally learned to put it away for awhile when I get to where I am sure it isn't what I wanted. (Also before I might be tempted to cut it into little tiny pieces!!!)
Mariah.