Press H on your keyboard. For more useful commands go to Main Menu -> Credits -> Help
The scenes you mentioned are cut scenes and don't appear in the album or sketchbook (the latter contains more artworks not shown in game). After I finished drawing all CG art, I had even more ideas.The cut scenes looked too simple to earn a place in the album. Besides, the album is already very packed.
For now you can only save those special scenes by screenshotting or save slot.