Nah, he's actually prevented from doing much, it's a very intense scene buildup but he just cuts them a bit before being "defeated" and killed. Actually, a lot of the Spanish public (including me) didn't like this ending because a very promising and supercharged bullying&revenge story ended up as a frustrating, almost "good triumphs over evil" film with an ambivalent "feel good" or at least "(poetic) justice has been served enough" undertone and Spanish audiences often mock that unless it's well-justified in the story development.
i'd even be willing to bet that the original script had a much different ending but ultimately the director or producers or whoever didn't want to turn bully victim "Cerdita" into the female half of a gorish "killer couple", being more inclined to make a point about fatphobia, bullying and such stuff
