The amount returned is equal to the amount of the excess, not the amount of the excess plus earnings. Nothing about the gains goes on your 2020 tax return.
The gains will be reportable on your 2021 tax return by entering the code 2 2021 Form 1099-SA that you will receive near the end of January next year. There is no 2020 Form 1099-SA that needs correcting as a result of any of this.
