No, that isn't what John said at all. I wish you would understand this point. John said:
Jesus did many other things as well. If every one of them were written down, I suppose that even the whole world would not have room for the books that would be written. (John 21:25)
Before he said that, John also wrote:
Jesus performed many other signs in the presence of his disciples, which are not recorded in this book. But these are written that you may believe that Jesus is the Messiah, the Son of God, and that by believing you may have life in his name. (John 20:30,31)
What Jesus DID, the signs He PERFORMED were not all written down (because there wasn't enough paper/papyrus/animal skins, etc. in all the world and it would take up the whole world to do that it was so vast and eternal). BUT, John said, these things WERE written so that we would believe that Jesus is the Messiah and that by believing we would have eternal life. Doesn't sound to me like John thought he left anything out of what God told him to tell everyone. I also doubt very seriously that ANY of the Apostles/Disciples would have forgotten to ensure we knew the truth God has revealed to us through WRITING it down. That's what they did back then. Being a scribe was a busy job. Eventually, the local churches had copies of the manuscripts of the gospels and epistles. They were precious and cherished. Long before then, the Jewish people kept scrolls of all the Old Testament writings and every synagogue had their treasured copies which they read every Sabbath.
The written word is powerful, sharper than any two-edged sword. The word of God is the Sword of the Spirit - the only offensive part of the whole armor of God (Ephesians 6:17). Nothing that man comes up with can stand against it.