Without looking at your code, I think that is a limit of your keyboard (maybe I'm wrong here and is your code). There are keyboards where you can press only two keys at once in some combination. Mostly the shift and control keys are an exception. So try to use the control or shift key.
"In order to save money, keyboard manufacturers often put many keys on the same "circuit" of sorts within the wiring of the keyboard. This prevents multiple keys in the same region of the keyboard from being pressed simultaneously. Sometimes it even prevents more than 2 keys at all from across the whole keyboard being pressed at once. Often the shift, ctrl, and alt keys are not within this limitation, so you can hold shift and press 2 other keys at once and it will still work fine."