Did the questioner's actions stem from boasting or showing off? Is he sinful, and his deed void, requiring him to seek forgiveness? Is his friends' viewpoint—that charity should not be public—more valid than his own, which aims to encourage others to give charity?

What matters in spending is the intention. So, if you intend the Face of Allah and to encourage people to do good by informing them about it, then you are right, and that is not considered showing off (riya') or boasting (fakhr). Showing off is performing an act of obedience or informing about it for a worldly purpose, or to seek status in people's hearts, or to seek worldly gains through deeds of the Hereafter. As for boasting, it is self-praise for one's qualities. Your informing about good deeds so that you may be emulated is praiseworthy, for whoever guides to good receives a reward similar to that of its doer. Likewise, it is recommended for someone who is emulated to show their good deeds so that people may follow their example, and this does not contradict the recommendation to conceal good deeds.