When you think your essay's done, make sure you give it one more pass, checking for errors in both content (faulty arguments) and form (bad grammar, spelling, etc.). No doubt your teacher will be grading you on completeness, and an essay doesn't exactly seem done if it's riddled with errors. It might be especially helpful to get a second set of eyes; you could ask your parents, peers or even a TA (in a college course) to take a look at your arguments and make sure they stand up to scrutiny. After that, congratulations! You've got a compare and contrast essay on your hands. Was that so bad?
For a shorter paper, the above might represent three paragraphs; if you are writing a long paper and have a great deal of information, you may choose to write about each point, A, B, and C, in separate paragraphs for a total of six. However you decide to organize, make sure it is clear why you are examining this subject. You might be able to compare apples and oranges, for example, but why would you? Include any insights or opinions you have gathered. And yes, in general, three is the magic number. While there is no hard-and-fast rule that precludes creating a paper based on two points, or four, or five, a three-point discussion is manageable, especially for complex or abstract subjects. At the same time, a three-point structure helps you avoid oversimplifying, especially when addressing controversial topics in which discussions tend to become polarized–right or wrong, black or white, for or against. Three-point treatments encourage discussion of the middle ground.