Just in case someone else still gets stumped on it:
It is possible to get stuck on the trinket in the yellow zone. The problem is that the only checkpoints which reset the 2-gravline just before the trinket are the three in the room below the 2-gravline. From those, it is impossible to reach the 3-gravline that unlocks the trinket without hitting the 2-gravline. The way back is blocked by the 7-gravline; the way forward requires hitting the 2-gravline at least once. If the 2-gravline isn't fully reset, you can't get through its room without hitting any checkpoints.
Thus, it's only possible to get the trinket on the first time you pass throught the 7-gravline. If you die or hit a checkpoint between that and getting the trinket, you can no longer get it. This applies even if you never unlocked the 3-gravline covering the trinket. So what you have to do is flawlessly get the trinket the first time you play the yellow zone. If you make any mistake, you have to reset.
It is possible to get stuck on the trinket in the yellow zone. The problem is that the only checkpoints which reset the 2-gravline just before the trinket are the three in the room below the 2-gravline. From those, it is impossible to reach the 3-gravline that unlocks the trinket without hitting the 2-gravline. The way back is blocked by the 7-gravline; the way forward requires hitting the 2-gravline at least once. If the 2-gravline isn't fully reset, you can't get through its room without hitting any checkpoints.
Thus, it's only possible to get the trinket on the first time you pass throught the 7-gravline. If you die or hit a checkpoint between that and getting the trinket, you can no longer get it. This applies even if you never unlocked the 3-gravline covering the trinket. So what you have to do is flawlessly get the trinket the first time you play the yellow zone. If you make any mistake, you have to reset.