As I hinted earlier, there's a special rule for indenting procedure definitions. You generally indent the body of a procedure a few characters (I use 3), but you don't line the body expressions up directly under the list of variable names.
Don't do this:
(define (double x)
(+ x x))
If you do this, a procedure definition looks like looks like a procedure call, or a normal variable definition. To make it clearer you're defining a procedure, do this:
(define (double x) (+ x x))
This makes it clear that the (double x) is a different kind of
thing from (+ x x). The former declares how the procedure
can be called, and the latter says what it will do.