Using the Force could easily make things worse
First off, using the Force to push or pull things in combat is much more difficult than in a video game and could leave a target open for attack. Keep in mind that in this case, there was an ally right next to Darth Maul as well.
Second, Obi-Wan is still relatively untrained (only just ready to start the Jedi Trials) and doesn't have a lot of experience. Interfering with a fight between two people that each have twice the experience may not be effective (they may react to counter what you are trying to do), and could cause a distraction or other catastrophe that does more harm than good.
Knowing that using the Force to push or pull things in combat is very difficult, and that he has less experience than either combatant, let's consider the risks for each of your solutions:
pushed Maul to the hole
When Obi-Wan force-pushed the Battle Droids on the Trade Federation ship, very little precision was required: he was pushing a Battle Droid down a hallway with no allies in the way. This time, the two fighters are very close together.
It could very easily push Qui-Gon into the hole too, or cause Maul to move in an unexpected way, which might open up his master to an attack.
pulled Maul's lightsaber (or other kind of distractions);
When Obi-Wan force-pulled Qui-Gon's lightsaber, it was stationary and a few feet away, and even then it took a few seconds of wiggling before he could grab it. But doing this on a rapidly-moving lightsaber, held by two hands for much of the time, from farther away, and in a split-second window of time would be far more difficult. He could easily pull the wrong thing (maybe Qui-Gon's arm or saber) or just cause Maul's saber to move in an awkward way, again throwing off Qui-Gon.
There didn't seem to be anything else in the room to use (no giant pillars to throw around), so he couldn't have used anything else for a distraction.
pushed his master away just before the lightsaber stab (after he got punched)
He could just as easily have pushed Maul into Qui-Gon. And if he was successful, Qui-Gon would probably be off-balance, making it easier for Maul to get another good stab in.
melted the sides of that panel to rejoin the fight...
Assuming that it wouldn't cause a dangerous burst of energy if it were suddenly disrupted, this probably would have worked, and would not have been nearly as distracting to Qui-Gon as the other things suggested. I submit that in the heat of the moment, it just didn't occur to Obi-Wan to try this. He clearly had tunnel-vision, since he spent the entire scene looking at the fight, and not his surroundings.
Ultimately, most of the options that Obi-Wan had might have made things worse. The safest thing to do would be to not interfere and just stay put, letting his more experienced master buy time.