All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
There is no harm in excusing yourself from informing your father about your donation, but it should be done with respect and kindness to avoid upsetting him. You are not obligated to tell him about it. However, if your father did not accept your excuse and became upset, then you should have obeyed him and informed him, as long as doing so would not cause you any harm.
Ibn Taymiyyah said: “A person is required to obey their parents in all matters that do not involve disobedience to Allah... This applies to situations where the parents benefit and the child is not harmed. Thus, If obeying them is difficult but not harmful (to the child), it becomes obligatory, otherwise it is not (i.e. if it causes harm to the child, then it is not obligatory.” [Summarised from Al-Fatawa al-Kubra]
Allah Knows Best.