Theif, This happens to everyone (or will happen to everyone). The only difference is you were big enough to admit it.
I've had a few, including going head to head with someone on down wind. Immediately I thought I had misread the pattern so I kept quiet but he/she was just in the wrong place or unaware they were over an airfield. Any way , I avoided and the other one carried on. Lesson learned, just because you are in the pattern does not mean everyone else is.
As Viper put it 'A good pilot will evaluate what has happenned so he can apply what he has learned' (and pass it onto others).