You didn't fail badly at all. Don't tell yourself that, you just didn't do as well as you had expected. Firstly, would it be a waste of time and effort to do those humanities subjects when you clearly want to go to Uni with maths, maths, phys and more maths? Or I can see your line of thinking that it might broaden your horizons whilst you mostly concentrate on your retakes. However, I would see more logic in JUST concentrating on retaking in college and pick up a part time job on the side or something. OR negotiate with them about taking your desired A Levels on the basis that you're resitting?
Anywho, I'm sure you've gone round in enough circles thinking about this. I'm in a pretty similar situation and it isn't much fun at all lol. But, the reason I replied is because I noticed the one thing that we had in common was a drive to be in a better situation. With that, I genuinely believe that things will fall in place with hard work. I have a dream, ladies and gentlemen!