If the tablet is has access to the Internet then you can recover your PIN by entering the email that was attached when you configured the device in the first place. A backup PIN will be emailed to you and you'll be able to unlock the device.
If that does not solve your problem, your other option would be a factory reset. Press Volume Down + Power until the device restarts and displays Recovery menu. Choose Wipe Data/Factory reset and the device will be reset to its factory defaults.