I'll assume that no other funds were deposited into this Roth IRA and there were no funds moved out of this Roth IRA and that you filed your 2021 tax return by the April 18, 2022 deadline.
The Average Opening Balance is the balance at the beginning of the computation period, the date on which the first of the excess contributions was made, plus the amount of your excess contributions. Assuming that there was no investment gain or loss between December 31, 2020 and the date of your first $100 contribution, the AOB would your 2020 year-end balance plus the amount of your excess contributions.
Yes, the Adjusted Closing Balance is the balance immediately prior to the corrective distribution.
Net Income attributable to the excess contribution = Contribution * (AOB - ACB) / AOB
The amount corrective distribution required to be made by October 17, 2022 is then Contribution + Net Income. If net income attributable is positive, you'll need to amend your 2021 tax return to include the net income, otherwise there is probably no need to amend except that you'll need to be able to provide explanation to the IRS if they question your excess contribution.
Section 1.408-11: https://www.law.cornell.edu/cfr/text/26/1.408-11
You can do whatever you want with the money that is distributed to you as your return of contribution, including using that money to fund a contribution for 2022.
