The point of the spell was for Harry to know which direction he was traveling in relation with his goal. With it being dark out, it will be extremely easy for Harry to wander in part of the maze thats in the wrong direction from his goal.
Harry is shown using the spell repeatedly.
‘Point me,’ he whispered to his wand, holding it flat in his
palm.The wand spun around once, and pointed towards his right,
into solid hedge. That way was north, and he knew that he
needed to go north-west for the centre of the maze. The best he
could do was to take the left fork, and go right again as soon as
The second time he uses it he had been traveling generally in one direction for a while,
Left ... right ... left again ... twice he found himself facing
dead ends. He did the Four-Point Spell again, and found that
he was going too far east. He turned back, took a right turn
and saw an odd golden mist floating ahead of him.
How does he determine he went too far east, when his wand points north? Most likely his current path he was on was leading east, and he determined he had been generally traveling east for a while now.
The third time he uses it we dont actually know where Harry is, or what direction he's headed,
He took a left path, and hit a dead end, a right, and hit
another: forcing himself to stop, heart hammering, he performed the Four-Point Spell again, backtracked, and chose a
path that would take him north-west.
He still believed he was south and east of his goal, most likely he had hit the south eastern corner some time ago and had been lost in the maze in that corner for a while.
After this he seems to start using it at every turn or fork,
Harry moved on, continuing to use the Four-Point Spell,
making sure he was moving in the right direction. It was
between him and Cedric now. His desire to reach the Cup first
was now burning stronger than ever, but he could hardly
believe what he’d just seen Krum do.
This leads me to believe the paths are not square and that he isnt taking just straight paths that lead N, S, E, W, but that the maze has curves and angles, which is why his point me spell is far more effective, in telling him which paths lead where.
He had a choice of paths up ahead. ‘Point me!’ he whispered
again to his wand, and it spun around and pointed him to the
right-hand one. He dashed up this one, and saw light ahead.
The Triwizard Cup was gleaming on a plinth a hundred
yards away. Harry had just broken into a run, when a dark fig-
ure hurtled out onto the path in front of him.
The first time he clearly knew where he was in relation to the center. The second time we can be reasonably sure he knew he was still south of the center and had been headed east for a while. The third time we can still be reasonable sure he believed he was south of his goal.
Then she spoke, in a deep, hoarse voice. ‘You are very near
your goal. The quickest way is past me.’
The sphinx smiled more broadly. She got up, stretched her
front legs, and then moved aside for him to pass.
‘Thanks!’ said Harry, and, amazed at his own brilliance, he
He had to be close now, he had to be ... his wand was telling
him he was bang on course; as long as he didn’t meet anything
too horrible, he might be in with a chance ...
We can see that Harry clearly believed he was still on the south side of the maze so when his choice between a north and a south path came up after the sphynx he choose north and it paid off.
As you've said this could lead him to go the wrong way if he had passed it, but luckily he seemed well aware of where he was in relation to the center.
JKR seems to have given Harry excellent spatial awareness, so that he could visualize how far in any given direction he had gone in relation to the middle and the start of the map.
In reality the use of a compass would not be much help deep in the maze for finding the middle, but it would allow you to know which direction you were currently traveling.