Chances are that you deserved to be grounded. Whatever you did, you need to contemplate why you're being punished in the first place. It may not be fun, but this makes you a better person.
If you sneak out to see your girlfriend and your parents figure it out, they wont trust you anymore. I can tell you from personal experience it sucks to have your parents not able to trust you.
edit: completely missed that
My dad grounded me for spring break. Here's the reason.
- I tell my dad i'm going to my friends house.
- My friends don't pick me up.
- My friends pick me up and my dad says I didn't tell him.
Nevermind then. Your dad is a douche and you should disregard anything he says.
It's obvious he's punishing you to feel superior.