I’m trying to get to chapter 4 but it’s telling me to decorate still. I have already bought sold..

You have to buy enough decoration to satisfy the Flower value indicated on the top right corner next to the flower icon. It will say how many more flowers you need to reach the next level. When you buy decoration, you must wait for construction to be complete and remove the red ribbon, before the Flower value to count. You can also get more Flowers added when you renovate landmarks, upgrade buildings, and send Jack on a delivery for flowers..

When you sell, you will lose Flower value and only get half the coins back that you paid for it.

When you store decoration, you will also lose Flowers, so you'll need more to reach the next level.