Sue S I am only seeing this post 8 days later so I would assume the discomfort has subsided.  Please do send me a private message if you are still in pain? you should not be and probably your diaphram is really tight.  You may not have touched into your floating ribs as you mention being careful.  This area can be chronically tight so it is possible you started releasing deep tension and it started to talk to you... I hope you are feeling better.

Liked the class but did have some floating rib issues ~ wasn’t careful enough!

Leah F thank you for the comment. Next time take care to stay off the ribs and use the position to stretch and elongate your body. another option is to deflate the ball so it is very soft, or use a smaller ball ( also soft - till your body adapts and is more capable and absorbing the pressure constructively)