You dont need to do A level law. You can do any A levels you want; the most important things is to choose the A levels you enjoy so you can motivate yourself to get the high grades you want. Honestly, although a level law might give you an insight in law, wider reading gives you more freedom and flexibility to learn about law. I personally wouldnt want to do law as an A level as I would feel that would be too stressful for me so I like doing stuff for law in my free time and it's given me the freedom to choose what I want to know more about than a more controlled curriculum to law. For example, ofc I would learn the compulsory modules for a law degree but there's so much you could learn - for example, I was interested in teh role of IA in the legal sector, which you wouldnt learn in a level law. Honestly, it's your choice and I think sticking to your original option would be good since you already chose it but if you want to do A level law, totally go for it. However, you wont need to know anything for law at uni as it will get taught to you so dont worry about the preparation for law until the summer in yr 13.