this feels more like a horror than anything even remotely romantic. I wonder if the author is that inept, or is legitimately trying to portray the situation as disturbing and incomprehensible.
This page and the next is an obvious sign.
This page, her comment on liking "transient things" is pretty big foreshadowing
This page and the next, mc is confused, she takes advantage of her trust
Her skipping school the next day, trying to behave normally, after realising what happened to her
GEE. IDK, I WONDER IF THE DISCOMFORT IS INTENTIONAL.
It most definitely is. It is indeed meant to be uncomfortable.
The scenes may be presented in an erotic manner, but it is by no means meant to be romantic and fluff.
The whole series so far just screams of "stranger danger", you gotta be blind and fooling yourself really hard if you're still convinced that it's a cute and sweet age gap romance. At this point, it's like some want it to be cute, and just ignore all the signs and are still confused at why does it not feel sweet.
Because it's not. Everything so far has been the adult making the main character feel comfortable and trust her, and finally taking advantage of it.
So, no, the author is not inept. They portrayed it as uncomfortable, most readers feel uncomfortable, and that's absolutely the point. (Though more specifically, it's like, "hot", and "wrong". The eroticism is built on how it feels wrong.)