Two revisions on this cross section.
Level 3 - Cross Section 3 (Paper 2)
My first thought was to raise the exit door and row of platforms to stop the player from being able jump up from near the entry door. This works but requires an extra section to be added to the left to make sure the player can still get up to the platforms.
Level 3 - Cross Section 3 (Paper 3)
Thinking again it would be much simpler to just lower the debris around the entry door, as shown in the third version above.