There is a difference between twisting the individual stitches (which happens if you knit them through the back loop), and when it says 'being careful not to twist' when knitting in the round. In that case it is referring to making sure that all of your cast on stitches are facing the same way, not twisted around the needle at any point, before starting to knit in the round. If that ever happens there is no way to fix it aside from ripping it apart and starting over again.
Emerybourne, now I'm wondering which of the above you meant when you posted your question? When I originally read it I would have answered the same way that Ingrid did, but now I'm wondering if you meant that your cast on got twisted before you started knitting and now it's not forming a perfect tube like it should?