The best way to convince your mum to let you do what you want is by proving how responsible you are. You should start helping her with chores, doing well at school and making up for mistakes to be able to win her trust. Moreover, you can also talk to her any time that you want her to get you what you like.
You need to understand children are suppose to do what they are told to do. Everything you think you want to do is not always good for you. Your parents know what is best for you. They can discern what is right, wrong, good, bad, wise and not wise. They are not saying NO!!!! ---- because they don't love you. When they say no, it's because they can discern the out come of what you are wanting to do. They are your covering. Do you know how many children parents let them do what they want? If your parents give you that choice your life would be a living hell. Please follow your parents. Look up the word discernment, that should help you to better understand why your parents say no!!!! The world is full of evil just ready to steal your life God bless you !!!!