Unfortunately, TurboTax's price for preparing a state return is not based on refund amount. I've had to pay for a state return even when my state refund was $0, or even when I owed state tax due.
If you've already paid and filed, then for future reference, some states have free state filing on their websites. And the IRS has a list of several ways to file Federal for free, and in many cases a state return for free.
https://www.irs.gov/file-your-taxes-for-free
