"The corridor goes 30' and terminates in a T intersection. At the intersection, the corridor to your right goes 40' and turns 90 degrees to the right. The corridor to your left goes on as far as you can see, but there is opening on the left wall 30' from the intersection."
Unless the PCs specifically take steps to do so, why would they be aware of exact distances?
Don't draw a map out, except where you need one for the tactical situation. What's more, unless they have the supplies with them and nominate a mapper, don't let
them create a map, either.
Include teleport traps, weird architecture, and other such traps to throw off their mapping efforts (you should provide some sort of clues as to what's going on, so clever players can spot it). Put them in situations where mapping is difficult - they have to flee from a monster and don't have time to count distances, they're about the be flooded out, they have to crawl through lots of infuriatingly narrow and winding tunnels (that all look alike). That sort of thing.
Failing that, how do I make them work hard to NOT be lost?
A better way is probably to use a Skill Challenge. If they have a particular objective in the maze, require them to roll a number of successes to find it. Failure gets them lost.
Then, another Skill Challenge to get out.
If they fail the challenges, put them in some room containing a tactical challenge (monsters or a trap), and have them deal with that. Then have them spend the next {time period} and let them try again. (The time period should depend on what resources they have. If they're using torches, it should be the duration of one such torch. If they're instead using an everburning torch or similar, make it day - and keep track of rations. And if neither of those work, deduct a Healing Surge.)
If they specified that they were keeping a map, that's good for at least one automatic success. If they specified that they were pacing things out, that's good for another one. And, if they've been diligent in keeping maps even when they get lost, grant them an extra auto success each time they fail the challenge (as the map gets better as they go).
Bear in mind, this kind of mapping can drag the game out. Make sure it's going to be fun/worth it for the time expense.
This is so very, very true.