How much teaching is expected on a CV for a graduating PhD student (mathematics)?
It is what it is.  Some schools give you less opportunity for teaching than others (e.g., schools in the UK).  

If you are looking for a research postdoc, then having a lot of teaching experience is not too important.  For instance, at my institution, we want to make sure you're competent and not going to cause problems, but you don't need to have won five teaching awards.  This is evidenced primarily by your teaching letter.  If you think you can get a decent teaching letter now, then I wouldn't worry about it.  (Note: if you're TAing now and probably won't be again before you apply, consider having someone who will write you a letter observe your class.)

If you're looking for a "teaching postdoc," e.g. a temporary position at a liberal arts school, they typically want more evidence that you're a good teacher, so you might try to actively look for more teaching opportunities.

Note: presumably many other students at your institution have the same issue.  Try finding out how much TAing recent graduates did and what kind of jobs they got after graduating.