There is no additional charge for fixing your return. However, if while fixing it, you need to add a new form or need to upgrade that will incur additional charges.
You should review your fees in your TurboTax account to find out what type of fee you are being charged. Sometimes you start with the Free Edition (which is typically a simple form 1040), but as you enter more complex forms or sections you might be required to upgrade depending on your individual situation.
To locate the fees section, view the link below
How do I review my fees in TurboTax Online?
To see why are you being charged or to remove any non-desirable fees, click on the link below
Why am I being charged for TurboTax Free Edition?