A lot of schools/colleges don't do psychology A level so there will be a lot of people at uni in the same boat as you. Which is why (I heard) that the first year of psychology at uni is getting everyone up to speed and onto the same level so it shouldn't hold you back/put you at a disadvantage. But you might decide it's not what you thought it would be and end up hating it or dropping out. Like the person above me suggested, it would be worth looking over some A level textbooks to see if it interests you.