Please help (year 12)

I feel really upset and I can’t focus on anything or really think about anything else other than the fact that I regret by subjects so much. I picked chemistry biology English lit and art because they were my favourites and I did well in them, I picked a wide range of subjects to keep my options open. However I realise I probably would want to apply for medicine, and also you need psychology as your third a level WHICH I DIDNT PICK. And I want my chances of success to be as great as possible since I have a uni in mind I rlly rlly want to go to that recommends psychology as a third subject WHICH I DIDNT KNOW 😭😭😭😭😭😭 anyways now I’m told there’s basically no chance of me changing eng lit or art since all the courses are probably full. I genuinely dknt know how I’m gonna focus in my classes when I know my chances of going to medical school are lowered by a stupid mistake. I also don’t really like English or art anymore I only tolerate them. I’m so upset 😭