I have skipped three piano lessons this semester. The lessons are one-on-one with my professor, and happen weekly. I get really nervous when I skip, and avoid the issue by not showing up AND by not emailing him. I absolutely need to email him ASAP since tomorrow is my performance final for the semester. This is a horrible situation that I totally could have avoided. Please give me a little guidance, or a lot of guidance on how to address the issue. Whenever I try to draft an email, I get emabarassed by how immature I sound. My behavior IS immature, and i can't believe I let it get this bad.
Suck it up and CALL him instead. Just say what you said here. It's credible. It's honest. "I've written you so many e-mail messages that I never sent because I was embarrassed at how immature I sounded. But that's not a surprise, because my behavior was immature."

Then you need to bridge to where you're GOING. "This semester was one of learning and I regret I didn't take advantage of every single opportunity I had to learn with you. I regret my behavior because it wasted your time and deprived me of a chance to improve." It's not what you expect of yourself and not a reflection of what you will be in the future. Please accept my apology and know that ... blah blah blah. But sincere!