Agigante comes from the verb agigantar, meaning to make something gigantic or to grow immense. It's a vivid and somewhat dramatic word that isn't commonly found in everyday conversation or many song lyrics.
In this song, the singer uses it in the line "Ojalá que no puedas hacer que tu piel se agigante de sueños" (Hopefully you can't make your skin grow immense with dreams). Here, it's used metaphorically to express a deep desire for her ex-lover to be unable to experience the overwhelming joy and passion of new dreams and desires with someone else, wishing him a lack of fulfillment in his new relationship.
Paola Jara's "Ojalá Que No Puedas" is a fiery anthem of a woman scorned, wishing her ex nothing but misery in his new relationship. She's not holding back, hoping he can't even kiss his new partner or look her in the eyes without thinking of someone else. The singer wants him to feel the sting of her absence, wishing that when he's with his new love, he'll be thinking, "Que despierten sus pieles pensando en la mía" [May their skin awaken thinking of mine].
This song is all about poetic justice, with the singer wishing he can't make love to his new partner, and that his skin won't "Se agigante de sueños" [grow giant with dreams] or "se muera de ganas" [die of desire] when he's with her. She even hopes his hands bleed if he touches his new partner's skin or hair! It's clear she believes she was the most important person in his bed, and she wants him to remember that. The song ends with a powerful declaration: "Y ahí, te acordarás de mí" [And there, you will remember me]. Talk about a mic drop!