You can also use the Device Viewport Zoom setting to scaled the output to the device. More info:http://ajarproductions.com/pages/products/in5/help.php#device-viewport-zoomWe're also considering the possibility of a full screen button in the future.
Update: Full screen is available in the Viewer Display Control Frame.
You can also use Desktop Scaling to scale on Desktop (and Mobile). More info:http://ajarproductions.com/in5course/?lesson=flexlayouts