I agree entirely with the above post. But musical expression is also an issue of technique. Technique is not simply the ability to hit the notes. It’s the ability to play them the way you want. When I teach students at the lower levels, the first couple of times we encounter a ritard for example it is uneven and lumpy. The slow down too quickly or too abruptly. So it’s a matter of practicing a controlled ritard and learning how to pace it. The same with a crescendo. The first time you try to do an even crescendo, the first few notes will be quiet and then abruptly the next ones will be loud. These are issues of technique. You have to be able to control how each note or each group of notes comes out. So you may have musical ideas that you want to express, but you have to have the control and technique to express them. Otherwise they simply won’t come out. My suggestion is that you focus as much on technique, especially etudes, as on your pieces, and when you play the etudes, fool around with dynamics and tempo so that you learn to control those things. Then when you go back to your pieces, you’ll have the control to do what you want musically.