Have you tried this:
make a global variable called CameraAngle or whatever, then set it's value to 0.
Then use these events:
On Left arrow key pressed:
Set cameraAngle to clamp(cameraAngle - 45, -45, 45)
On Right arrow key pressed:
Set cameraAngle to clamp(cameraAngle + 45, -45, 45)
Every tick:
Set Camera angle to cameraAngle