i just use the portal after the glitchted part and nothing is happening help pl
Using the repaired portal is the end of the game! However, if the screen you got was almost entirely blank then you got the lame ending, which means there's still puzzles to solve and things to find! You'll have to restart from the beginning to go again but once you know what to do it's not hard to get back to your previous state.
There are 8 cube bits in the game, and they are all obtainable ;)
There is one which you cannot get by jumping - you have to solve a puzzle to reach it.
If you already got an ending without collecting them that means you found at least one of the *other* main collectible type in the game - Anti-Cubes. Those are separate, and equivalent to a whole cube.