Difficulty in calculatiing GSTR3B output tax due to multiple revisions in invoices

Hi,

As per the attached table I yet to file my May 2020 GSTR3B, due to corona issue I need to give discounts and waiver to my client and unfortunately I got their confirmation only on September 2020,

In compliance point of view I have already paid taxes for rents not received for April 2020. Me being a starter to GST can some one please help me to solve my case as per the attached excel sheet to correct my GST tax liability for May 2020 and how to calculate fine for one invoice which I missed for March 2020.