John Tucker Must Die (2006) on Netflix

Plot summary

Kate Spencer has spent years feeling invisible, moving whenever her mother Lori's latest boyfriend leaves them both behind. In Portland, Oregon, she catches the attention of three girls who until now have kept to separate crowds: overachiever Carrie, head cheerleader Heather and activist Beth. What they share is John Tucker, the school's basketball star, who has been dating each of them in secret while telling each one that she is the only girl. Kate, who has watched John's double life from her waitressing job, is the one who points out that the three of them are not each other's rivals. They ask for her help, and their plan is to turn Kate into the girl John cannot resist, so that she can then break his heart.