Firstly, it’s important to be positive. You may not have done as well as you wanted to or could have done, but it’s not the end of the world. You can always re-sit various modules and even the whole A-Level if necessary.
Also, while you may not want to redo a whole year, when it comes to it, it may be for the best. Really, in ten years you won’t even care about the fact you redid a year – There are many people in Britain who redo a year or two, and it isn’t the end of the world. (Many actually regret not redoing a year when they had the chance.)
So just be positive, don’t dwell on the fact you may have failed your exams (or didn’t quite get the grades necessary), and if necessary, simply redo the year.