Dear Quetzally,
We are so excited and impressed that someone your age is interested in providing such a valuable service to your community! It sounds like you will need to engage in some advocacy. First, I would suggest reading the Toolbox chapters on Organizing for Effective Advicacy -- Chapters 30 through 35 and Toolkit #10.
You will also need to engage some adults in your efforts. You might start with your City Council representative or other elected official representing the area where the park is located. If this is a City park, it is something the city will need to address, so find out who to contact there as well (for example, in the Parks Department). You might also check to see if there is a teacher at your school who would be interested in helping -- for example, someone who teaches government classes.
Good luck with this effort, and please write again if you have more questions.
The Community Toolbox Advisor