Lord Flash-Hart.
Sorry to hear that OASC didn't go according to plan. I am sure that there are many on here who have far more experience and advice to give, but I'll throw in my thoughts to get the ball rolling.
Would it be worth considering, between now and your next attempt, trying to fit in some Adventure Training either in the UK or overseas. As a student I went away to Belize for a three month Expedition with Raleigh International. Aside from the fact that I had a great time, saw a bit of the world I wouldn't have seen as a tourist and had a break from my studies, I genuinely feel the experience improved a lot of my personnal skills. At the end of the exped, I returned to the UK with a better understanding of my own strengths and weaknesses, improved confidence and a real understanding of what teamwork and leadership really mean. You can try to simulate challenging situations in the sterile environment of a hangar or work through exercises with a pen and paper but there is no substitute for first hand experience. There are a growing number of charity organisations out there that run expeditions to far flung corners of the world, so it may be worth having a look and see if any take your fancy. At the end of the day, even if you come back from an exped completely unchanged (highly unlikely), should you get asked at OASC what you did to improve your chances, "I help build a school in Bangladesh" or "I lead an exped through the Andes" is bound to impress. Just a suggestion and I am sure there are far more people on here with their own thoughts and experiences, but it may be worth looking into. Good luck and keep smiling...