Pants on Fire - Meg Cabot

But she can't exactly tell the truth, either--not when she's juggling two boyfriends, secretly hating the high school football team everyone else worships, and trying to have the best summer ever. At least Katie has it all under control (sort of). Her biggest secret, what really happened the night Tommy Sullivan is a freak was spray-painted on the junior high gymnasium wall, is safe.

That is, until Tommy comes back to town. Katie is sure he's going to ruin all her plans, and she'll do anything to hang on to her perfect existence. Even if it means telling more lies. Even if, now that Tommy's around, she's actually--truthfully--having the time of her life.