Are you currently using the CocoonJS launcher? or are you using the Cloud Compile?
My guess is your using the CocoonJS Launcher.
The Launcher is use to do developement testing and not publication. C2 ability to lock orientation is never garunteed on mobile. However in CJS you can at the game selection screen click the GEAR ICON in the top right corner. There will be the option for "Portrait/Landscape". Expoloring software is fun.
If you were using Cloud Compile. Then it's in the browser feature options and is required that use the check box. But I'm guessing your using the Launcher.