Helpful general tip for navigating: Each room has walls with force arrows on them near one of the entrances. Those arrows indicate which exits will be available if you enter the room on that side.
Anyways, turns out there was another similar step earlier.
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×Enter 3N1E from the south, then go east to 3N2E, then go back to 3N1E. This lets you leave to the north, and continuing on that path leads to the branch I mentioned earlier.
If you can't find your way there, here's directions starting from 1N:
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×-Exit north to 2N
-Exit east to 2N1E
-Exit east to 2N2E
-Exit south to 1N2E
-Exit west to 1N1E
-Exit north to 2N1E
-Exit north to 3N1E