Can you confirm where you have set the resolution in Xibo?
If you select the Display Settings option in your CMS, click the down facing arrow at the end of the Display Setting row you wish to change (Windows for Windows players etc) and choose Edit from the drop down menu, this will take you to the Edit Profile window. Next click the Location tab. This is where you can set the resolution for the Player. If the Width and Height fields are currently zero, you will need to set them to the correct resolution for your screen. Make sure the Top and Left fields are set to zero to ensure the layout displays across the full screen. You will need to restart the Player device for the change in settings to register.
If you have already done this and you are still having the same issue, please let me know.