You've got to take the initiative and play your game. In a decisive set, confidence is the difference.
If you can react the same way to winning and losing, that's a big accomplishment. That quality is important because it stays with you the rest of your life, and there's going to be a life after tennis that's a lot longer than your tennis life.
Find something that you're really interested in doing in your life. Pursue it, set goals, and commit yourself to excellence. Do the best you can.