You must not be afraid of playing wrong notes. Just forget it, play it wrong! But play!
I'd like to share one idea with you.
Your mind dictates the quality of every moment of your experience.
And yet, many go through life ignorant of what determines the character of their minds. You are not a thinker of your thoughts or an experiencer of your experience; the self you identify with is an illusion.
The mind is all you have, and analogous to muscles, it can (and should) be trained. Through the practice of meditation you can discover the unintuitive facts about how it works.
By realizing that I was lost in thought, I have learned to be present. To play.