Hello, I'm sorry to hear you are having trouble.
Checking this at my end, everything appears to be working as it should and I can see from others' comments it appears to be working for them, as well.
Is it possible that you either downloaded the demo instead of the update (the demo would have the Gallery, Endings, and Extras disabled)?
Or I know the demo and game files can sometimes interfere with each other if they are in the same place. If you have not already, please could you try downloading the game file again into a different folder from the demo, and see if you still have the problem?
In the full game, the extra scenes are under 'Extras' and 'Kickstarter backer scenes'
Many thanks for playing