Distortion at Nadir and Zenith of 360 Panorama

Hi All, 

I used my drone to take a group of images that I stitched into a 360 panorama in Lightroom.  I imported the panorama into Photoshop, then added more sky so that the panorama was twice as wide as it was tall.  I then put the panorama into a website that will allow you to rotate the 360 spherical panorama (facebook will do this) but the nadir and the zenith of the panorama are distorted as shown in the attached image.  How can I fix this?  It looks like there aren't enough pixels to fill in the bottom, so the image had to be stretched to fill it in.  I included two nadir photos in the set that that panorama was stitched from.