Both unilateral and bilateral contracts are enforceable in court. For example, a unilateral contract is enforceable when someone chooses to begin fulfilling the act demanded by the promisor. A bilateral contract is enforceable from the get-go; both parties are bound the promise.
Yes, scratching is a form of self harm. Try to tackle this problem while you can because it has the potential to get worse. I started out scratching and now I burn myself with a lighter and cut myself. It's a self-destructive way to deal with overwhelming mental/emotional pain.
Other kinds of self harm are: burning, picking at skin, biting, pulling hair out (Trichotillomania), hitting/punching yourself, scratching, small overdoses, poisoning, excessive nail biting, sticking things into your body, swallowing inappropriate objects, banging your heads or throwing your body into something hard.