Everyone makes mistakes-even your boss.
Has the invites gone out yet? If not, it can always be corrected. If it has, maybe you can notify people of the corrected date via email?
Having anxiety and depression skews our perception of things. Yes, your boss may be annoyed but maybe not to the point that he wants to fire you. It also likely that mistakes like this has happened before.
I don't think you should resign. Wait and see what your boss says.
Post Edited (ForeverPositive) : 8/14/2019 6:47:22 AM (GMT-6)