I am stuck for days between 320 and 321 it keeps telling me to decorate. What do I do?

If you cannot get to the next level and the game says to "decorate", it means you need more flowers added to your island to proceed. On your island screen in the top right corner, next to your current level, it says how many more flowers are needed for the next level. You can acquire flowers in one of the following ways: buy decoration, renovate landmark, get from Jack's delivery. If you buy decoration, the flowers will not count until after construction is complete and the red ribbon is removed.