I'm sorry for taking advantage of everything you gave me.
I'm sorry for wasting the money you spent on me.
I'm sorry for wasting your time and effort.
I'm sorry I'm not anywhere near what you wanted me to be.
I'm sorry I couldn't become what you expected.
I'm sorry I don't listen to you.
I'm sorry you had to spoil me.
I'm sorry I turned out like I did.
I'm sorry I don't teach my sister.
I'm sorry I snap at her.
I'm sorry I don't clean up after myself.
I'm sorry I cry.
I'm sorry I'm not good enough.

I really hope that this could make you feel better.
Because I never ever wanted you to be unhappy. I never wanted to disobey you.
I'd take it back if I could.
Because I love you. I really do.