If you have the money... book it in to get whatever you can repaired. Even if it can't be done before your parents get back at least you've been responsible enough to start to fix your mistakes. Or find someone reliable who can do a damn good job.
If you don't have the money then obviously you're gona have to grovel and promise to pay him back.
Either of these will be better than lying, as they probably won't believe you anyway. If you're honest, it'll blow over quicker than if you haver to lie for the rest of your life.
So dude, how did you do it?