i have given my A level economics and cashed in but i did not get a good result

I had given my a level economics A2 and was planning to start my university next january, all the 4 units had been given, but none of them came out well so i am planning to give a re-sit, but i have also cashed in and unit 4 economics is not available in january, what should i do? i had a descent mark in unit 4 , is there any ways to cancel the cash in?