For a jump scare to work, there are several parts, the sound, the timing, the environment, and the image/animation (or at least that is how I see it). Any of them alone won't be enough. Even if I had a super scary-looking image, it won't work without sound. My timing was inspired by 2 different things. One of them being the scary maze game, and the other thing is the escaping the prison game (part of the Henry Stickmin collection). If you know both of those, you might know what I am talking about.
The scare timing was intended. When the narrator talks to you, it gives it a feeling of a casual game that you can play all relaxed, but the environment is a bit more horror-like. It gives a mixed feeling of relaxation even in a dark place, which I thought would be a good environment for an effective jumpscare because people wouldn't generally be prepared for it (unless they read the comments).
As for the rest of the text, I might put it after the jam rating session is over on the game page. I think my game has been spoiled to whoever reads the comments anyway, so I would prefer not to directly add the text until after the jam (because no further spoilers). Ironically, it is my comments also spoiling it though.