Scenes unlock as you progress in June's Journey. If a scene is still locked, your Flower level might be too low, or you might not have collected all clues in the previous scene. Or both.
For example, to unlock Scene 3, you need to be Flower Level 3 and you must have found BOTH clues in Scene 2.
To earn more Flowers and increase your Flower level, you must improve Orchid Island. Build or upgrade buildings, decorate with decorations, or renovate landmarks to earn the Flowers you need to unlock the scene.