Why did you start rubbing your palms in the first place. Did you start because you thought you might wake up if you didn't?

If you are rubbing your hands in order to prevent yourself from waking up then you're doing it wrong. You rub your hands to engage yourself in the dream world. There should be no thoughts or worries about waking up. That thought alone is enough to wake up you and no amount of rubbing will prevent it.

Like DreiHundert said, you need to stay calm. Stay focused only on immersing yourself in the dream.

And since there are no natural laws in your dream world there is no guaranteed continuity from one dream to another. A stabilizing technique may work in one dream and then not work in another. If a dream doesn't work out the way you want don't always assume you're doing something wrong. Sometimes a dream will just end. Accept it and look forward to the next.