How can I go on a date without my parents knowing?

I want to ask this girl I know out to a movie (and I'm pretty sure she'll say yes) but I don't want my parents to know. I don't necessarily want to lie, just "stretch the truth" a little. Her name is Sam so I'm thinking I can just say Sam (instead of Sammy or Samantha) so they think she is a guy. I am not going to ask her out until school starts again (in September) so I don't need an answer right away, just be sure to answer in the time allotted! Thanks.