Improving piece that is already polished

I have two competitions in two weeks from now, and I would really like to do my best (and possibly win them). I am playing Tchaik, and I have been pretty unmotivated to practice it, because I have been performing it for over 5 months and I don’t know how I should be working on it if it is already polished. Unfortunately, I do not sound like a professional when I am playing though, which obviously would raise my chances of doing well. Any advice for what to work on? how to improve from a more advance-student sound to professional?