So earlier today, my husband saw from our QuickBooks that we are getting a penalty for not paying Q3 taxes
Without intending to sound rude or fallacious, who cares what Quickbooks shows? You're done with the business. All you "may" need to do is to print a final year income/expense report.
For example, In QB select REPORTS, then Company & Financials, then Profit & Loss Detail. Click OK to open the report. Note in the upper left corner of the report the default for Dates is "This fiscal year to date". Change that drop down to "Custom". Then to the right of that enter 1/1/2020 for the From Date. Then for the To date enter one day after the last day of business, or one day after the last day of a recorded income or expense; whichever is later. Then print that out and that is what matters.
