Integrating a customized module as a panel in the Opportunity creation view, similar in appearance and behavior to the Revenue Line Items (RLIs) panel

I created a new module called Contract Offices, which has a one-to-many relationship with Opportunities. The creation appears to be successful, as the Contract Offices subpanel now shows up on an Opportunity record.

However, it's not appearing during Opportunity creation the same way as the Revenue Line Items (RLIs) panel.

Does anyone know how to?