I sneak out of my backyard all the time and spend almost all day with an older friend.
Why do you have to sneak away to spend time with your friend?
My parents forbid me to go off the property.
Sneaking out as a child can be dangerous. Your parents may have had good reason to keep you home and you should obey their wishes.
I did nothing wrong in my mind, so I don't see the problem.
As a kid, there are dangerous things out in the world and your parents are trying to protect you from them, so its not right that you disobey their wishes. Stay at home until your parents feel it is okay for you to be out on your own.