Interesting scenario to play what-if with, and a good lesson in the problems of identifying friend (or fool) or foe.
You are presumed to have acted reasonably if you employ deadly force against someone who has
unlawfully and
with force entered your habitation...but the young man enter unlawfully or with force? He may have deceived the maid on purpose, which might indicate unlawfulness, but he may have really been mistaken. And if the maid let him in with a key or pass card, did he really enter with force? hmmm. Had you "drawn and pressed" after one more step., would you be in the legal right? moral right? Tough scenario. If you had actually bagged the fool, I think in the end you probably would have come off OK legally, minus perhaps some lawyer fees and plus some gray hairs, but you might not feel all that good about it.
Expanding the scenario slightly, I have been given keys/pass codes by the front desk to rooms that were already occupied. If I sauntered in and didn't see you immediately...until you started to draw...what then? I would certainly argue that I did not enter unlawfully or with force. I would
especially argue that if my draw and press were faster than yours...
Would the calculus change if this were midnight instead of noon? You were asleep instead of awake talking to your son? If it was a woman that walked in? etc. Oh, this is an excellent training scenario.
Glad you came out OK in the end, and hope the wedding goes well, and hope you can calm down enough to enjoy it!