If you’re a high school junior or senior, you’re probably working hard to get into college–researching schools online, preparing applications, taking grueling SATs and ACTs and writing the perfect essay. Maybe you have an air-tight application. But you could still blow it, with something you thought was harmless fun: Your online profile. Whether it’s through Friendster, Facebook, MySpace, Xanga or LiveJournal, you better have an air-tight online profile, too. High school guidance counselors are warning juniors and seniors this year that their online profiles could make or break them in getting that “yes” answer from a college of choice.