Having the same problem getting to level 31. On the left it shows 30 on the right I have over 300 flowers?

You probably need 300 more Flowers to reach level 31. Add Flowers by buying decoration to meet the criteria. Each decoration has a set amount of Flowers, but its Flower value only counts after the construction is complete and you remove the red ribbon. The higher the Flower value, the further in the game you can progress, and the less likely you will run out of island space. You can also add Flowers by upgrading buildings, renovating landmarks, sending Jack on certain deliveries, and completing certain Memoir scenes.