From my understanding, law is one of those few careers where going to a Russell Group university gives you an advantage over people that don't, as law firms tend to hire primarly from RG universities - but they also hire from non RG unis so going to de Montfort wouldn't be the end of the world. However, if you're not particularly keen on it and you think you can do better at A-Level, I think it'll be worth it for you to resit them and reapply!