Is the money I received - 900 dollars - in exchange for training that I claimed to have completed, while I did not fully complete the agreed-upon training and without the knowledge of the American granting entity, lawful or unlawful?

It is not permissible to take these funds, and they must be returned to the association, as the agreed-upon conditions must be adhered to, for the Prophet, peace and blessings be upon him, said: "Muslims are bound by their conditions." What you did is fraud and deception, and it is forbidden.