Replying to Mom Against Skiing

Hi NS, let me start by introducing my self. I am Jack, I am from minnesota and I am a senior in highschool. The snow and season here are both just starting to fall into place. We have got a decent amount of snow now and I want to make a jib in my backyard. My mom is the only problem, she will not let me build it because of my grades in school (which by the way, are not even that terribly bad, i have all B's and a one or two A's and C's) so she said until i get my first semester report card back in january she will not let me build anything. What should I do?