It's not a failure H, it's a minor set-back.
I don't think you need to strip down all the paint, probably just sand down the white, and have a good, long look at the rest, and think about how you can correct any errors. One of the hardest finishes to achieve, probably the hardest, is a metal finish. It has to be done carefully, and, after practice with the airbrush, you should be able to achieve at least a passable bare metal finish. No disrespect to aerosol spray cans, but they aren't the best tool for painting a relatively small model - large scale R/C aircraft, and cars, maybe, but not a 1/48th scale fighter. This is more true of a metal finish - believe me, over the years I've tried all sorts of things to get a good metal finish, including an aeorsol - once!
So far, the model is going reasonably well, especially considering the total number of models you have built. However, and don't be upset by this, I do think that your enthusiasm is causing you to rush things a bit. It's too easy to get carried away and want to move on to the next stage; this is how, and when, mistakes occur. Jobs are partly spoilt, parts are lost, or masking, for instance, is forgotten. It's happened to us all, and will continue to happen occassionally, so it's nothing to be ashamed of!
The thing to do now is sit back, maybe get on with something else, and then plan what needs doing, and in which order. The minute you (or anyone for that matter) open the box to start on a new kit, that is the time the planning starts. You should be looking right through the instructions, checking ahead for possible problem, or tricky areas, seeing if certain parts can be left off until later, to aid construction and painting, and avoid possible damage. Look at the various stages, and ask yourself questions, like 'If I do this, will it effect that' or 'OK, that bit can be added later, if I do xxx, as it'll make masking easier' and so on. It's a bit like planning, and implementing, a combat patrol!
Herr Doktor Professor Wojtek has the perfect statement concerning modelling, when he says it's not a race. It isn't a race, the only time element in a GB being the four month period each GB runs.
Think of it as if you were building a house to live in. You wouldn't throw up the bricks (or whatever) then slap some paint on the result, just because you wanted to see the house, the place where you are going to live, finished and standing there all built and painted. You'd want to make sure that every brick was properly set, the walls straight, the roof sound, and the paintwork pristine. Like building a house, modelling takes as long as it takes; it's not a race, it's a hobby, which should be enjoyable. Yep, we all get frustrated at times, and sometimes well p*ssed off, but that's life!
Throwing the model in the bin won't achieve anything, so have a think, and then get back to it when you feel the time is right. There is absolutely no reason that I can see why that Mustang can't turn out to be a very nice model. Look at the tools you've accumulated, and learn how to use them - they won't work by themselves, just sitting there. Practice with the airbrush, learn how the compressor works, why there might be a flow problem, spitting or whatever, and how to overcome it. Then, try painting a 'scrap' model, or an old coffeee cup, anything, in the desired colour scheme, just to see how it works out. When you're happy, then tackle the 'real thing' - it's got to be done sometime!
Cheers, chin up, and don't give in!!