I think then that the rest of essay would come together if the intor and the conclusion were fixed.
That is an important observation! The into and conclusion frame the essay and provide its structure. Topic sentences are quite important in this way, too.
You might want to move this sentence fro the beginning of para #1 to the beginning of para #2: Colleges showcase the different perspectives that students bring from around the world.
It has nothing to do with the rest of paragraph one! Paragraph one is about how you came to this decision about what you want to do. Move that first sentence to the start of para #2, and then add a sentence to the end of paragraph one. that will make it so that the sentence where you list the topics of the essay will be in the middle of para #1, and you can END para #1 with a thesis statement that gives a THEME to go with the paragraph topics.
Get inspired, think of what that theme is, and add it to the end of paragraph one. It is a theme that involves your background, school environment, and volunteer work.