Unfortunately that is the only way you are going to improve. If you are serious about your dancing, you will have to put in a little more. What you have to be careful about though, is not to practice in bad technique. All the time that you are practicing you have to concentrate and make sure that you are doing everything the right way.
If you want to know how to improve ballet, it is a good idea if you get a book or a video to help you. Looking at pictures of the right and the wrong way to do everything will help you to see where you are going wrong.
I found that going back to the very beginning and practicing each step from the very basic to the level where you have to be is the best way to go. Get every single step right from the beginning and work from there.
If you are wondering how to improve ballet, it is important to concentrate on the correct posture and turnout as it is the basis of ballet. Do not force anything though, because it can result in bad mistakes. A turnout will only get better with time as will all your other techniques.