Overall, this is an excellent start to a compelling essay. Keep in mind that although the committee allows you to write up to five pages, three double-spaced pages is usually adequate. Feel free to add more detail, but make sure your text is concise and transparent. You might consider "writing" ideas and then "rewriting" them. Too often, authors put ideas onto the page, but do not render those ideas compellingly. Giving your sentences a bit of extra effort, and giving your experiences a bit of extra reflection, will result in a persuasive essay that compliments your accomplishments and character.
The popular "topic of your choice" option had been removed from the Common Application between 2013 and 2016, but it's now back again for the 2017-18 admissions cycle. Use this option if you have a story to share that doesn't quite fit into any of the options above. However, the first six topics are extremely broad with a lot of flexibility, so make sure your topic really can't be identified with one of them. Also, don't equate "topic of your choice" with a license to write a comedy routine or poem (you can submit such things via the "Additional Info" option). Essays written for this prompt still need to have substance and tell your reader something about you. Cleverness is fine, but don't be clever at the expense of meaningful content.