It's going to be bad if he misses and hits someone else instead. They're SSS agents, so of course they'd check the victim and/or have them checked at the hospital.
So they'd find the needle mark, the needle, the tranquilizer in their bloodstream, wonder where they came from, and would point at the only foreign entity who was present at the party.
I can see so many ways that watch could backfire.
1. shot at yor , but she catches it causing her to think there is an assassin nearby Making her even more nervous.
2. hits yor and combines with the alcohol in her system causing her to get even more flirty with lord for more romance hijinks.
3. hits the brother but doesn’t do shit cause of that bloodline.
4. hits the director but then yor does some of her usual drunken craziness at the same time, that results in someone going flying into the director taking the blame for knocking him out.
I love how Loid figured out Yuri was the biggest obstacle to a clean getaway, so he decided to kill him through PDAs with Yor. And how everyone just accepts Yuri is weird and rolls with it.