Kant's Deontology Analysis

Let's say that a murderer kindly knocks on your door and you opened it. The murderer attacks you with an axe and your fight or flight response kicks in. You decide that since your life is in danger and there seems to be nowhere to run, you choose to defend yourself. The moment the murderer closes in for the kill, you deliver a jump kick to the chest, killing the murderer instantly. You wonder what would Kant's deontology say about self defense? In my understanding of Kant's categorical imperative, the first maxim of universality suggest that any action you do as an individual must be acceptable as a whole. In other words, choosing to defend yourself when you're being attacked should be an acceptable thing to do because you know at some level