The "Due" column is part of the Progress Invoicing feature in Estimate form. Although you see Due column on the screen, when you send out Invoice, the customer will not see that Due column. You can click Print or Preview at the bottom and see it.
If you really don't need this partial invoice feature, you can turn this off from the Gear Settings. (Gear icon on top > You Company > Account and Settings > Sales > Progress Invoicing > OFF).