This happened to me also. I took psychology and it is just so different from what I expected and not my thing at all.
I am at the end of Y13 now and I did continue with it, something that helped me is having a friend who does find interest in it. When studying with them it's a bit easier to forget about how much I don't want to do it, it also helps to try to link it to things I do find an interest in or just in general to life. I suppose it will depend how applicable your subject is to everyday life though.
If it's an essay subject you might have a bit of freedom to somehow bring your interests into expanded answers, which sets you apart from other people anyway.