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 (SH) or deliberate self-harm (DSH) includes self-injury (SI) and self-poisoning and is defined as the intentional, direct injuring of body tissue most often done without suicidal intentions. These terms are used in the more recent literature in an attempt to reach a more neutral terminology.