Registration items are displayed on two pages. The Register Page and the Sponsorship Page. What dictates what item is displayed on which page is controlled by two toggles when editing a registration item.
Under the General tab and under the Options you will see:
Display On Registration Page
When enabled, the registration item will appear on the Register Page.
Display On Sponsorship Page
When enabled, the registration item will appear on the Sponsorship Page.
If an item is not showing up where you want it, check these settings and adjust as needed.