You'll most likely need to file an amendment for both returns.
It's possible that you're entitled to an exception from filing Form 8833 with your federal return. Please see Exceptions on the IRS' Claiming Tax Treaty Benefits page for information.
However, if you don't qualify for an exception, you'll need to amend your state and federal tax returns.
Please see the IRS' Instructions for Form 1040-X and California's Amend an income tax return page for guidance.
