I'm a completionist in most games, though sadly, I have not managed to complete a game (like the Dragon Age games) 100%--meaning doing every side quest, collecting all of the mosaic pieces or whatever there are to collect in the game I'm playing.
I'm don't think there is any way to "100% complete" ACNL. There is more to the game than just completing the catalog. Completing the catalog doesn't seem like much of an accomplishment on its own since it doesn't really require skill as much as it requires a ton of patience and persistence.