I figure you're either not having the command_continue definition in your Scene_End class (check Scene_Title for that, it's a seperate definition starting with the line 'def command_continue'), or you renamed it somehow. Either way, it doesn't reference it.
In case you just put command_continue in there, you might wanna check out some tutorials about classes and subclasses, or simply try to figure out by yourself what's the difference between 'class Scene_Title < Scene_Base' and 'class Scene_Title'. Don't take this as aggressive critisism or anything, just trying to point you in a useful direction in scripting ^^