How to act when you're caught cheating?

ok so in science today, i had a test. i found one question really difficult, and my study guide right there in my desk. so, i decided to cheat. unfortunatley, we had a sub today, and our sub actually watches us. she caught me, and called me out in front of the whole class. the kids forgot quickly. after the sub walked back to her desk(with my study guide) i saw her jot something down. i have never cheated before, and i think im gonna be in a LOT of trouble come monday. i even changed my answers after i got caught cuz i felt bad!! i just want some advice on what to say when i get in trouble, and what to expect when i get in trouble!!!! PLEASE HELPP!!!!