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?