It's likely there is an overscan issue with your TV or Xbox One. You can compensate for this in the Xbox settings.
- Open up the Settings app.
- Go to General - TV & Display options.
- Select "Video fidelity & Overscan".
- Make sure "Apps can add a border" is ticked.
If this did not work, you will have to check if "overscan" is enabled in your TV or screen's settings. If enabled, you will have to disable it as this will allow you to see the whole window. This setting is screen-specific so we recommend checking your TV/screen's manual to find out how to disable it.