: so i was on a spaceship full of humans after shutting down durandal's core, i
: almost got squished by a big corkscrew near some water, and found a
: terminal, which went on and on(with the poetry and everything) and then
: told me to "try again" and sent me back to mountaineering g3. is
: this normal, or did i screw up somewhere?
You screwed up the first time you played G3 Moontanning, but you were supposed to screw up. Unlike other nonlinear scenarios such as Rubicon and Fell where a mistake can lead to a bad ending to the game, Eternal always gives you a second chance. Moontanning is a timed level. Remember the first time through when you reached the end and were told that you hadn't shut Hathor out in time? You then played a couple of levels intended to make up for your mistake and, in the end, helped Durandal to escape the Universe. Without Durandal to warn humanity about the Pfhor, the Pfhor took Earth by surprise and the level with the spaceship full of humans was a glimpse of that very unfortunate future - the total enslavement of humanity. Better luck next time. Finish Moontanning as fast as you can and you'll get a very different message, and a chance to continue in the successful timeline.
Note - this sort of thing will happen in each and every chapter of Eternal, so be prepared for a lot of deja vu.