Just a wild guess, but if full VR is showing a cinema screen that’s static as if it was cinema mode, perhaps you’ve got edge peek toggled on. Check what its hotkey is and press it while using fullvr mode.
Edit: also if you haven’t already, check the image zoom setting in the ingame vorpx menu while in fullvr mode, this causes the view to fill the screen or viceversa, also make sure the proportion is 1:1 so there isn’t any letterboxing. If you’re playing on G3D mode and can’t move around there’s also a position unlock setting.