Hmmm, some ideas for titles. Some are pretty lame, but they're included to maybe inspire a better alternative.
What I Want for Myself and My Life: (insert character name)'s EssaySimple enough. This would be a possible title if the story is entirely first person in the girl's view.
Do With Me What You Will
This could be either 1st or 3rd.
The Essay
The simplest title available-- right to the point, nothing clever.
Five-thousand Words
Or, round up to the words in the essay to the nearest 1,000.
The Girl Who Was Good At Being Bad
Terrible, very cliché, but I included it just because it might give you better ideas.
Over the Knee
Perhaps if you get in the girl's head a bit as she's in position and anticipating that first glorious slap on the ass, you can use this title to capture that mood.
Spank Me
Something obvious.
Spankee
Ugh. I hate this one, but there it is anyways.
Anyways, without reading it, and at the crack of dawn (for me anyways), this is all I could come up with. Good luck!