first gen fire stick wont go full screen calibration

Just got a 4k tv and my first gen fire tv stick won’t calibrate/stretch to fit full screen. There are black borders that won’t go away. Is this normal for the first gen fire stick on a 4k 43 inch tv? It doesn’t have any problems on our other tv’s that are 720 and 1080. Even in Kodi, when I adjust the zoom, there are black borders left no matter what I do…