A square map isn't very natural or interesting to players. To finish the map, you'll use the terrain tools to customize the edges of the map to make it look more like an actual island.
Opening the Terrain Editor
All terrain, whether it's mountains or painting grass, is created using the Terrain Editor.
Before starting, publish your experience so far. That way if you don't like how your changes turn out, you can easily go back to the saved version.
Go back to the top-down view (click on Top in the corner widget). This will help you edit terrain better in the next page.
From the Home tab, open the Terrain Editor.
