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.
Self-harm is when somebody intentionally damages or injures their body. It's usually a way of coping with or expressing overwhelming emotional distress. Sometimes when people self-harm, they feel on some level that they intend to die. Over half of people who die by suicide have a history of self-harm.