Hello @legacychimera247, this reads like the feature request at #7486, which mentions that Big Picture mode is currently locked to a 16:9 aspect ratio and likely the same root cause with your 16:10 display. Feel free to add your experience to that feature request.
Closing as a duplicate.
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Your system information
Please describe your issue in as much detail as possible:
Simply enough my screen resolution is 1440×900 but in big picture i only have 1440×880 maximum, so i'm having black bars. How do i put big picture in a way i don't have black bars anymore?