If you have upgraded or added features to your TurboTax Online Free return, then you will be charged for those upgrades/additions. Unfortunately, there is no way to downgrade or remove the extra features. You would need to create a new return to go back to the Free product.
You can go to the Return Manager (under Tools) and start your return over in TurboTax Online Free. Then once you have started your new return, you can go back into the Return Manager and click the small Trash Can next to the unwanted return to delete it.