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-Injury (which occurs when someone cuts or burns or otherwise harms themselves) is one of the harder behaviors associated with mental illness for people to fathom. People mostly understand (I think) when someone becomes psychotic, gets stuck in a deep depression or has mood swings.