Here is a list of suggested steps to help with your issue of not having a full screen display on a second monitor:

1. Confirm the monitor is disconnected from the presentation.
2. Ensure the correct display outputs are correctly connected.
3. Check the presentation is set to a compatible resolution.
4. Open the presentation in a single window.
5. Select full screen mode.
6. Update graphics card drivers.
7. Ensure that the presentation is on the correct monitor.