Yes, you will need to amend your 2020 return to make this correction. However, TurboTax won't have availability of Form 1040-X (amended return) until 3/25/2021. I'll link a TurboTax FAQ below that contains instructions for you to amend your return. Please follow the instructions carefully; they are quite specific.
Nope. It is free to amend your TurboTax return.