Depending on your version of Sage, and your security rights there is a reverse journal entry option in GL.

In Sage 100 2015, a Journal Reversal button was added to the Transactions tab in Account Maintenance and to the Journal Drill Down window. Click this button to perform one-click journal reversals. The reversing entry is created, and a journal comment is added noting the reversal. You must print or preview the entry in General Journal Entry before updating it.

Note: In Role Maintenance you must select Allow Journal Reversal on the Security Event tab to enable the button

1. Go to General Ledger, Main, Account Maintenance (enter account number to reverse the transaction)
2. Click on Transactions tab
3. Highlight the transaction you wish to reverse and click Journal Zoom button or double click transaction
4. Click Journal Reversal button
5. Open General Ledger, Main, General Journal Entry
6. Verify the posting date is correct (this date should be the same date as the journal posted incorrectly - 11/11/2020)
7. In the Reversing Date field enter 1/11/2020 (this will post the original entry to the correct date)
8. Print or Preview the General Journal
9. Click Yes to update the General Journal

If you want to get a restrict posting to future period you can select "Restrict Accounting Date to Current and One Future Period' option in Company Maintenance.