You should be getting the OT pay. If your contract says 22 hours a week is full time and you teach 23 hours for 2 weeks, then you should get paid for the extra hours. I would definitely mention it to them. "It evens out." is not correct. You should be paid for the OT. The trick is how you approach it.
If you approach them in the right way, then you'll get the back pay. Just don't be a jerk about it. I agree the teacher's class will probably disappear soon, but you still should be paid the extra. Even if it's only 2 hours a month.
If you let them get away with something, then they will try to go further.
I personally would approach them with a comment similar to "I am wondering when I will be paid for my overtime. Do you know?" If they came at me with the "It evens out." Then I would say something like, "I'm pretty sure I'm supposed to get OT pay for anything over 22 hours in one week, but I'm not totally sure. I'll double check my contract and let you know. Thanks a lot for your help."
Then, a couple days later, I'd bring my contract up and show the clause to them.
It's your decision though. Just telling you what I would do.