Looks like this for me on my browser.
Nothing you did wrong there, it's intended to happen for the story that MC gets screwed over there as we saw since Sheila became so jealous about MC going all the way with the other chick who in the end turned out to be the volleyball girl from school. And Sheila didn't touch that "fat blob of trash" and she didn't end up getting covered in mancream either, as it's showed and explained there that the fat blob hits himself in the dick multiple times before he jerks himself to ejaculation which knocks him out, and Sheila then covers herself in some french fries dip sauce/mayo to make the manager of that burger joint to think that she made him cum even when she didn't so that she would win the graduation contest instead of that other chick who MC ends up banging in that contest.