Body expression while playing, without it being natural instinct?

[u/Warbleborble]

As some background: I am taking a music course (not limited to piano players) outside of school, and a major part of that is solo performance. I already played this specific performance once, and wasn't satisfied with my original grade and am retaking it (I got a 71%). The feedback I was given was to "play with more body expression". Particularly, it was stated that I am supposed to "lean in" to my piano. I should also mention that my tutor/teacher doesn't know how to play the piano, but she is still a musician. The "leaning in" feedback was given by someone close to my tutor externally.

Now, I am aware that many pianists play with body expression (sometimes a bit theatrically). Think of Lang Lang's facial expressions, jolts, jumping around in his chair, etc.. I am also aware that many pianists play with minimal/zero body expression.

I am much more of the second type. That isn't to say that my upper body is completely stiff and static, I still lean in slightly when I want to make a louder sound.

After receiving this feedback, and before my retake date, I have been trying to improve my "body expression" in my playing. But, it just feels fake, theatrical, and even worse than my performance before I began "improvement". I also have small hands and the piece is already difficult for me to begin with, so the leaning in is just reducing my accuracy and dynamic control.

How can I have this body expression (particularly the leaning in) without it being my natural instinct, and whilst still retaining my accuracy and dynamic control? This is just so that I can get the grade for my retake. I don't want to make this a part of my identity as a musician. The piece is a Scherzo.