Push your ass back against him.

Instead of struggling, you subtly rub your ass back against his cock. Perhaps this will distract him so you can get loose.

"Hey!" Sean yells. "This fucking sissy's rubbing his ass against my cock!" Your face burns and you are consumed with shame, but your own dick is also rock hard. Sean keeps grinding his cock against your ass while continuing to immobilize you with his arms and legs.

"I think I should get to fuck her," Sean says to Coach Donovan.

What? Fuck her? You're not a girl, you're not gay, and you're certainly not going to be fucked by this asshole in front of the entire class. And you assume there's no way Coach Donovan would allow it.

Coach squats down to look right into your eyes, which are starting to well up with tears of shame and humiliation, and says in a quiet voice, "Parker? If you want to say no, just say no, and I'll stop the match."