Getting everything is rather simple, but if you need some help I'll explain the system.
The true end is unlocked by getting AT LEAST two points while a special scene is unlocked by getting all four points. You get one point just for playing, then another for every "correct" choice you make afterwards. The "correct" choices are: 1, 1, 2.
If you've already gotten the true end, just pick the opposite of what I said and you'll unlock the bad end :P