Can I fill out turbo tax federal form just for the purpose of filling a state return? Will I get charged for both forms since my federal is already filed?

Yes, you can fill out your federal form for the purpose of transferring that information for state tax preparation.  However, you will not be able to e-file state only.  You will need to print out your state return and file by mail.  For more information, see the TurboTax FAQ below.  https://ttlc.intuit.com/replies/4232481