Problems with creating 360 Panorama - it is not flat as expected

[magdalenej26098593]

I made a panorame out of 26 pictures of my dji mini 2

it is a mulit row shot.

Some panoramas looked well when i murged them but this is not correct. 

How can i ensure straigt panoramas with the same shot procedure. (Sphere quickshot in DJI)

Attached you find a picture with title "as expected" and one with "not as expected"

Who can support - who has any idea.