If you've created a google account, after several tries you can see at the bottom it will ask "forggot pattern?" You can then enter your email and password and it will ask to set up a new pattern
If you haven't, I hope you've backed everything up because you have to do a hard reset of the phone, it will wipe your phone of all data but you will solve your problem.
To do this,
1. Turn the power off. Remove and replace battery.
2. Press and Hold the Volume Up, Home and Power button.
3. When the start up screen show, release all the buttons.
4. Use the Volume Up/Down button to navigate to "wipe data/factory reset"
5. Select "wipe data/factory reset"
6. Select "Yes -- delete all user data"
* Allow several minutes for the factory data reset process to complete.
7. Select "reboot system now"
* Allow several minutes for the reboot process to complete.
If the information is important to you, you can recover data from an app located here:
http://www.recoverandroid.net/samsung-galaxy-s2-file.html
You will have to purchase the app, however.
Here is a video of how to use the program
http://www.youtube.com/watch?v=3HWLGBMmx7Q
If you have any further concern please come back and we will continue to assist with your troubleshooting needs.