No, it's fine how it is. You won't be able to see through it when the car is on the track. If you put too much paint on it will make the body too heavy, and the car top heavy. The paint will also crack easier if it is thicker.
yeah you can almost see through paint when you hold it up to the light but on the car it looks fine. Yeah what speedo said is very true about the car getting top heavy its the worst place to add weight