You're teacher's probably right... Because they're not technical errors, their cause must be in your thinking as you play. My guess is you're focusing too much on the details of your playing such as note-by-note or mechanical aspects (you shouldn't need to think of what you're fingers are doing if the technique is good, it should be subconscious). Microscopic detail is good in practicing, but it's too much to think of in performance.
But the mind has to think of something.
What I would do is try for a broader focus. Instead of thinking about the notes, think about the phrases, sections, overall structure. Instead of thinking about what the fingers are doing, think of the keys, or even better the sound.
So I would agree that it's a balancing act. I don't have a concrete answer, I'm exploring it myself, but I find that as I learn a piece my mind focuses more and more on the big picture, and to trust my subconscious to handle the details. Thinking of the details causes overload, and weird mistakes.
Some of the pieces that I know really well, it's like all I have to do is decide I want to play it, shake my arms and music comes out with the greatest of ease.