G68 is modal and should stay in effect until cancelled by G69. That being said, the rotation can sometimes become stacked. I noticed that a g code file I was using would rotate an addition 90 degrees if I stopped the code mid-run, rewound it, and then tried again. I can't say that's what you're seeing, but it may be a funny effect of G68. If you'd like to post your g code, I can take a look for you.