Your way forward for the moment is to tackle the issue of getting your mom to agree to you attending dance at school/college or a dance class/group, while at the same time maintaining your excellent academic performance.
The first step in any successful negotiation is to understand the point of view of the person you are talking to, so get wise on what is going on in her mind.Let's say she is fearful that creative/performance careers are tough to get into, knowing that only the very best will get there, and that often it is very important to have a back-up plan so that you can pay your rent and other bills when you're an adult and leave home. This is practical, however she may also have an emotional desire to see you happy and successful, she may have struggled in her own life to achieve status and recognition and wants this for you.
Ok so this is her- next we come to you and what you want. Focus on something you want to achieve in the next few months- a class or group, maybe once a week? Get all the details so that you have the information at hand - where , when, costs etc. Think through how you will present this to your mom- how it will benefit your career, your education and your well-being. For example, it is well known that students who work hard and excel in academic studies, also need to have work-life balance by doing an activity at least once a week that gives them relaxation and enjoyment. Students who fail to attend to this have been known to experience stress, low self esteem and poor physical fitness, which has a negative impact on their academic success.
If you present your argument in this way, rather than getting into a massive emotional argument about who rules you, you'll be more likely to get what you want.
There will be time in the future to settle this argument, you will be an adult in a few years, for now win this battle.
Step by step you'll get there! Best wishes x