What do you recommend me doing if my math instructor isn't very good and I know I can learn the same content better elsewhere?
Or he might go out of order and teach us chapter 6 when we're suppose to be on chapter 2. Up to this point he hasn't done anything like that and has actually been very good at keeping on schedule. 


So why do you think he will do it? In your question, you do not give any examples of what he does wrong. Be careful not to become overconfident and think you know better than anyone, this might come back to bite you in the future.

If your issue is that you feel that the course is very slow, and you want to learn faster, then you are doing the right thing: study on your own at your own pace.

If you really feel that the lectures do not bring you anything, it is your decision whether you want to skip them. Assuming there are no attendance requirements, no one is going to stop you. This is university, you are responsible for your own decisions. 

Make sure that you are ready for the test though. If the course provides access to past exams, that is a good way to gauge if you know the content that is going to be tested. If the professor uploads his slides, that will also help you know what was taught. Otherwise, it might be worth asking a classmate what the professor is covering. 


  I might accidentally study something he's not testing us.


I do not see how that would be a problem. If you learn more than strictly required, good for you.