If you’re really short on time, and if it’s just for a school graduation thing, I would recommend using commercial music and putting their credits at the back of your project (unless you really want to submit it to festivals, but you mentioned you’re short on time…)
The reason for using music that’s already available is that you won’t have to worry about whether your score is good enough or not. By collecting a number of commercial music (or score), you could listen and see which one fits your project best. Because in the end, the emotion evoked from the music that matches your project is one of the most important aspect. Once that’s done, and if you have free time, you could then make your own score, apply it to your work and then send it off to festivals 
One suggestion for making your own score is this (I read this from CGI Filmmaking: The Creation of Ghost Warrior - by Timothy Albee):
Pick the music/song that you feel fits your project. Once you feel comfortable with the mood and the flow of the music, make them your own that’s similar to what you feel when listening to the commercial one.
[Quoted from the book]
“This temporary score will help you get in the mood of your piece. As you grow accustomed to hearing the different musical bits with your piece, you’ll probably feel the need to change pieces here and there. You are narrowing in on the final feel for the music that you will eventually create. When you compose the final score or purchase the royalty-free loops you will string together in a program like Acid Pro or Cool Edit Pro, you’ll know the different feelings and nuances that you need your tone poem to elicit.”
“As mentioned before, the temporary score is the music that you lay into your animatic to help you get a better feel for flow and timing. This will also help you figure out what kind of music you will want to have composed for your final piece; you’ll be listening to it a lot over the course of production. This is the music you must replace with your own original or commisioned score before releasing your film!”
Unless you’re already an accomplished score-writer, then ignore the above comments…