The only way to unlock your ipad if you forgot your passcode is to do a restore from ITunes:
How to Unlock an iPad with a Passcode
The only way to unlock an iPad with a passcode, other than entering the passcode, is to "restore" it to its original factory settings.
To restore your iPad -- which deletes all of your data (songs, photos, videos, apps, and so on) on the iPad use the following directions. Be absolutely sure that you have backed up the content on your iPad before restoring it.
Apple's official instructions to restore an iPad are:
1. Connect iPad to your computer.
2. Select iPad in the iTunes sidebar, then click the Summary tab.
3. Click “Check for Update.” iTunes tells you if there’s a newer version of the iPad software available.
4. Click Restore. Follow the onscreen instructions to complete the restore process. When restoring, it is recommended that you back up iPad when prompted. When the iPad software has been restored, you can choose to set up iPad as a new iPad, or restore your music, videos, app data, and other content from a backup.