I'm kinda confused... I have beated game, but story only shows 85% complete. How can I get it to 100%?

Mostly I would go back to the worlds that don't have 100% and some of it means getting all the keyblades and the portals

Do you have every cutscene and all that? It sounds like you missed a lot.

Or is this like 100% journal completion?

Mini games, Secret bosses, cut scenes, treasures. You'll need to do all these.

Do you have every cutscene and all that? It sounds like you missed a lot.

Or is this like 100% journal completion?

 

I'm kind of sure I have every cutscene.

Isn't there a journal or something that shows what you have and dont?

Try beating the secret boss and the portals.

I read somewhere online that in order to complete the Story 100% that you had to collect every spirit and defeat Julius. But you already have. So it may just have to deal with your spirits. I hope that helps.

Most likely missing treasure chests, commands, trophies, support abilities, incomplete spirit boards and thus a lack of all the possible attacks.

Your journal shows you what you have in most cases, you can google for the complete list and use it as a guide to what you don't have, then go about getting it.