Well if you are frustrated- shelve it. Then in a few models down the road, after gaining more experience, maybe strip it back with oven cleaner and then try again. Also buy some metal tracks for it in the mean time and then use those. All is not lost- just maybe time for a break from it. Don't throw it against the wall just yet!
I like how you went back in with the yellow in the airbrush- good job there.
But I have to say I think the red and green are too light and frankly I don't think you got a good match there.
But like I say- early days still and man you keep getting better and better, so that in time I'm pretty sure if you decde to revisit this one- you'll be able to make it look stellar!