Hi,
if you see a grey area at the top of bottom of your photo-sphere it means that your 360 picture is not a spherical projection, but a cylindrical projection. This means that the top and bottom part of your picture does not exist to create a full photo-sphere, which causes the grey area.
Spherical panoramas (you can look fully up and down):
Width to height ratio is near 2:1, e.g. 6000x3000, 8000x4000, 9256x4628
Cylindrical panoramas (you cannot look fully up and down):
The width of the image is at least twice as many pixels as the height of the image, e.g. 6000x2500, 8000x3999, 7500x3000, 8888x4443
To fill the grey areas, you can either upload a 2:1 aspect ratio version of the picture or replace the grey area with other 3D items of your choice.
Cheers,
Stefan