On the “Embed options” when editing your game, there are options of how the game is displayed, including this:
[ ] Fullscreen button — Add a button to the bottom right corner of your embed to make it fullscreen
Have you tried this? It would potentially allow the users to go fullscreen if they want to. There are also some options there to set the size of the canvas, is that what you used to change the game to “270x480” ? That sounds like a very small size, maybe it would be better if you set a bigger size instead?