The goof items below may give away important plot points.
In the Timothy Cavendish "happy ending," he is writing the screenplay for the movie based on his adventures. The typewriter text shows a phrase containing the word "labored". Being English, he would most likely spell it "laboured".
In the end, two moons are shown close to each other in the sky. One of them is full, while the other is crescent. As they are close to each other and reflect the same light sources, their phases should be the same.
There are no known habitable planets from which Earth would be visible in the night sky. However, this storyline is set hundreds of years in the future, by which time a good deal of technology may exist. The "planet" in the final scene could be an asteroid or other fairly large celestial body on which Terra-forming technology is used.