Ugh, record horizontal video with your phone, dude.
Looks like fun flying. There's a ton of empty black video, then a few scrap scenes at the end; maybe you didn't set the export-to-video limits right?
One thing I want to try, actually, is similarly dangling a separate camera. I have a Ricoh Theta that can produce 360ºx180º spherical photos on an interval basis, and it stitches really well. If it dangles upside down, it would almost entirely hide the Mavic and make shots that the Mavic can't quite produce due to the gimbal's upper limit.