How to not be trash at deathbombing?

I play rn touhou 7, trying to 1cc reimuB on normal, but i always lose my last life at Yuyuko's last spellcard, cause im bad at deathbombing
I even try bombing when i feel like i will get hit but sometimes i lose a life anyway because i notice that one bullet
So now im wondering on how to get better at deathbombing since in mainline touhou after getting hit you have 133ms to use bomb and my avarge reaction time is 184ms

Deathbombing is a beginner's trap. You will never "get better at it" so to speak, nor should you try to. It's not a parry from a Souls game, or anything. It's a completely unreactable window in every game except IN (and PCB Reimu) for a reason: it's merely a sort of leniency "Coyote time" window for making bomb usage seem a little smoother. If anything, you should take it a deathbomb as a warning that you are bombing too LATE and that the game just gave yo a break.
Runs are not usually made or broken in one single interaction like failing a deathbomb here or there, they're usually built (or die) on a thousand little things.
It's far more productive instead of fix broad strokes that help a lot more like having a solid early game and having a good idea of what you think you should be bombing ahead of time. That's the kind of skill set that actually gets you runs and is even useful across games.

Play the game as normal, but the dirst ting you do when you see the you died/you're about to die is MASHING THAT SPACEBAR (or whatever you have bomb set to, i play on a controller)