text: Registered Nurse here; Okay hun, first of all 450 sit ups is far to many for your age or anyone's.  This does prove your in excellent physical shape.  Now you need to give your body time to grow and catch up.  11 years of age, your body is just beginning to mature.  Things may not come together all at once as you would like for them to, but believe me they will.  Now doing 450 setups, sounds like you could be developing another problem known as obsessive compulsive disorder, in other words, you over compensate, and work your body for to hard.  Slow down, exercises in moderation.  Please don't obsess over your body.  \nThanks for the opportunity to address such an important question.