It's possible that you added some additional services, such as Plus benefits or Live Review, or you completed your return using a different version of TurboTax such as TurboTax Deluxe or TurboTax Premier.
To review your fees, you can follow the instructions in this support article.
Also, you may have been required to upgrade based on what's on your return. Click here for the information on who qualifies for TurboTax Free.