My friends convinced me to run on our school's
cross country team instead of running on my own.---- I think it will be clearer if yoiu specify cross country or track, if that is what you mean...
Okay, I had to stare at this for a long time before I figured out what I think the area-for-improvement is. It is at the end of the first paragraph. You leave me thinking, "Okay, so what is the point of telling us that you neglected the important things?" So I want to see if you can add a thesis statement to the end of that para, one that intrigues the reader by telling the moral of the story, the lesson to be learned:
...watching television instead of embracing the experiences that would later define me. (Add a sentence that hints about what this essay will amount to).
Para #2
During my junior year...
In answer to the questions:
Any length between this length and about 500 words will be great. Don't make it too much longer.
In order to make it not-longwinded, you have to know your purpose. This is true in every essay, research paper, argument, interview,... everything. Know what you are trying to achieve. I think you are trying to write something that will make the reader feel inspired because of the enthusiasm and seriousness your writing reflects. So stay specific, and include only sentence that help achieve your purpose.
About being off topic: it depends on your purpose. Any content can be right or wrong, depending on what you are trying to achieve. But the focus of the essay is up to you. Right now you have a theme of retrospection and noticing what was important... it is cool, because it shows that you know what is important now.
No need to expound it year by year. Just expound it int he way that most strongly affects the reader.
Should I focus and explain in detail more on how I've benefited from what I did later in my school career (such as running with the team, community services, & being a teacher have changed me for the better)?
Not necessarily more detail about the... details of the experience, but maybe more detail about the plans you have made for the future based on what you learned.