@Gswho723
Even though my Android is locked in Portrait Mode, watching movies on the Roku Channel through the mobile app seems to automatically place it in Landscape Mode, thus giving me full screen viewing.
Try seeing if changing the "Device Orientation" of your Android device helps with the full screen issue. Maybe set to Automatic or Landscape.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102