When you see the green/white text on top of the screen, with the voice saying "Captain, are you ready for pushback ?" you are not supposed to confirm, it's just a message to get your attention.
Instead, if you reopen the GSX menu when Pushback is in progress, there's an option to *Cancel* Pushback, with a menu with two choices, 1 means "Yes to Cancel", so it will reset everything, and 2 means "2 No, don't Cancel".