OPTION 1: On paper, like the girl in the story, draw your world in detail and color or paint it.
OPTION 2: Create a 3D world - use a cardboard box (cereal box, shoe box, or other), draw or paint the outside of it. Add onto it using the "cardboard attachment techniques" below, or draw or paint the inside of the box.
OPTION 3: Describe your new world in words. Imagine the world in detail in your mind and thoroughly describe it so someone reading it would be able to see what you are seeing. Think about using art words in your description (words that we use a lot in art class - like line, color, tints, etc.).
Robert Smithson "Spiral Jetty" 1970
If you have time remaining in art class; use your pencil and coloring supplies to draw your 3D nature artwork on a 2-d surface (paper).