How can I persuade my mom to get me into Aikido cles?? ? ???

I like it and like want to go to Aikido cles ,how to persuade mom?And also dad but eventually mom is more important I have been in so-ooo many other things ,ballet ,piano ,KARATE ,Hip-hop ,and bellydance. All of them I quited ,now I am learning guitar and french.My sister has been with me in ballet ,KARATE ,and bellydance.I DON'T want her to be in Aikido.I think she is kindda like a part for me like to quit ,I don't feel like really comfortable learnin stuff WITH HER she might want to learn tap ,if I am willing to I wish for her to learn too ,but us NOT TOGETHER ,different hours ,or days of the week.What can I do or say so she WON'T want to be in it ,I want to scare her about it cuz she is like sensible .Main question: how to persuade mom and dad to get me into Aiikido cles? By the way my mom says ''You sometimes want everything ,but then you quit''.