The store hasn`t finished updating yet, you have to wait until it finishes before it will be free. I would like to add that the updates don`t happen at the same time for everyone, it finishes usually between 6 and 8 PM eastern, but it is possibe for some people to download it before the update is every where.
I was excited to hear that Don;t Starve was coming to ps4. Especially because it's supposed to be free for PS+ members! But when i downloaded it some minutes ago, the store charged me for the game! I demand a refund!