Good choice on piece I like that one

What makes you think you are playing an "easier" piece? Every piece is hard in it's own way whether its tempo that is the hard part or getting the write touch or bring out a main melody above a counter melody.
The pieces that the other competitors are playing will have different challenges for them. The judges aren't going to pick the winner based on who plays the fastest (I hope), they will more than likely be judging on who gives the best interpretation of their chosen piece. So don't worry about being "outclassed".
It's normal to be nervous it can be a good thing to make you play better. Besides why should you be nervous? They should be nervous!
What you need to remember is don't worry about the pieces the other competitors are playing that's not your concern. They have their own challenges they need to face and you have yours. You're playing something different to them, something which requires a whole different interpretation so you can't even compare. Just concentrate on your work and forget about everyone else.
Another tip, don't worry about what people in the audience are thinking, the more you worry the less you can concentrate on playing. Treat the audience as one person not many different people.
To play the piece better and to perform better, well when you practice try to focus more on areas you're not quite 100% and remember to use a good technique when playing. Remember the style of the music and who wrote it and the background of it. Show the judges you understand the music. This piece isn't just a show off piece it's more than that it has some very nice melodies you will want to bring out and play clearly.
hope this helps