Love Between Enemies by Molly E. Lee

Zoey Handler is ready to put an end to her decade-long rivalry with Gordon Meyers. They’ve traded top spot between valedictorian and salutatorian for years, but all that’s over now. Right? But after a crazy graduation speech prank gets out of hand, suddenly their rivalry turns into all-out war. Time to make peace with a little friendly payback.
Step one? Make him believe they’re now friends.

Step two? Show him the time of his life at an epic graduation party.
Step three? Don’t fall for his tricks.
Step four? Absolutely, positively, do not kiss him again.
So what if he’s cute? (Okay, hot.) So what if he’s charming? (Heaven help her, tempting.) So what if he apologizes? (That has to be fake.) She knows the real Gordon. And no matter how much her heart begs her to stop, there’s no turning back.