“…how do I write an intro/body/conclusion for an essay so short?” Ahh, you’re mistaking this task with the expectations of high school teachers.
You need to clear your mind and answer two questions: What do I want to try in college? And, how will I meet this, at this college? Then count. Then add relevant wording. (The specific thought questions may change, but you get the idea.)
But, these colleges are rarely asking for just a “point and shoot.” They usually look for the rest of what comes through: some intellectual curiosity, openness, more than just what preps you for a career, etc. And your knowledge of what the college offers (again, not just courses.)