So, I returned to the game and this time made it to the end!
I have to say knowing that I can resupply with oxygen really turned this game around for me. Now I could explore the ducts AND leave for a resupply when needed. This created some really tense moments where I wasn't sure I had enough air for a return trip, and in the end I had to rush blindly forward in hopes of reaching the end this one time, and it turned out the right way, I jumped down and scrambled to the canister - this felt really great.