One song

After my writing class pretty much made me hate the idea of writing short-fiction stories, I've been thinking a lot about what I want to write. I have a ton of ideas that would make great stories and I'm sure I'll get to write most of them one day if the fates allow.
In my down time I've been watching a lot of movies and two got me really thinking.
The first was "Walk the Line". When Johnny Cash is at an audition, in hopes to record his music, the producer he's playing for tells him to stop. The producer ask him if he got hit by a truck and you only had enough time to play one song before you go, one chance to tell people what you really feel about life, is that what you would sing? That's not an exact quote but you get the idea.
Then I was watching a favorite of mine, Rent. Roger, a song writer, is trying to write one song before he dies. But if you only get to write one song, what do you write about?
This all got me thinking. If I only have time to write one thing in my life, do I want it to be some lame vampire story that I only wrote because it met the requirements for my class? Do I want my one story to be written how my professor instructed so I can get an A? I want it to be written the way I feel it, I want it to say what I want it to say?
I just don't know what that is.