Have you checked your keyboard and/or adapter can handle 3 keys at once?
I couldn't get god mode to work so plugged my keyboard into my laptop.
I checked the following combos
"p" = "p",
Left Shift + "p" = "P",
Right Shift + "p" = "P"
and then Both Shifts + P which gave me nothing.
So it may well be a hardware problem. I assume if that is what it types on the screen on my laptop that means the Xbox isn't getting the whole message. I'll try a USB keyboard that's plugged into the desktop and hopefully it works but otherwise I'll need to finish the level properly. I could quite probably have done that in the time I've taken trying and testing this.