Probably got it too close to the camera.
Move your quad 100 units away from the camera, and scale it (x*100 (distance from quad to camera), y*75 (for 4:3 aspect ratio)). That way it'll more or less exactly fill the screen.
Move your quad 100 units away from the camera, and scale it (x*100 (distance from quad to camera), y*75 (for 4:3 aspect ratio)). That way it'll more or less exactly fill the screen.