She doubles down, and busts

Hermione frowns, looking disappointedly at the quaint hub her baby self has just grown, “Fuck, you’re not gonna be able to fuck anyone with that!” She swirls her wand again, invoking the spell again just as before, and adding for extra measure, “Engorgio Permanente!”

She smiles with satisfaction as she watches the mass balloon to a much more reasonable size. Hermione nods at her younger self, who is still blissfully unaware of the events around her, and she spins the Time Turner to return to her normal time.

Had Hermione put a bit more thought into her plan, she might have recognized that a flaccid dick looks much smaller than an erect one, especially before puberty reveals it’s true length. If she had, she might have tuned down the massive length she had given herself, and given herself a much less intense childhood.