Greetings!
I think you've just freaked yourself out a little by waiting til the last minute. Relax, and remember that it is easiest to write about something you are very familiar with, especially in a descriptive essay. Do you have any hobbies? Let's say, for example, you like to create your own videos and upload them to YouTube. You could describe, step by step, how you go about doing that. Or perhaps, one summer when you were a kid, you helped your mom grow cherry tomatoes (like I did). You could describe the hot sun baking into the earth, the distinctive scent of the tomato vines, the soft plop of a ripe, warm tomato falling into your hand. All you really have to do is envision that "something" with which you are so familiar, and the description will start to come to you. Don't sweat it--first, engage your memory, then just start to write!
Good luck!
Thanks,
Sarah, EssayForum.com