As a TA, what should I do about an error in the professor's lecture?

Here is the somewhat awkward situation.

I am a TA for a class that I have never taken before. The professor (probably) knows this, but I don't think the students have caught on, since it is a lower-division class and as a graduate student I have significantly more mathematical maturity than most of them.

As a TA, I am responsible for preparing the lecture notes for the class. A different TA is responsible for grading assignments.

A few weeks ago, the professor made a (small) mistake in his lecture, and I transcribed the error onto the lecture notes without realizing it was a mistake.

Recently we had a midterm, and the other TA noticed that a lot of the students were making the same mistake. The other TA recognized it was wrong and is now docking points for the error, even though I told him there was a mistake in the lecture notes.

What should I do? I think the students will be mad when they hear about this, and if I tell the professor, he might get mad at me for preparing bad lecture notes.