Horribly wrong, like certain Satie compositions (4-6)
I believe the answer is:
pear-shaped
'horribly wrong' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for pear-shaped that I've seen before include "Fat at one end and thin at the other - all wrong!" , "(Go) horribly wrong; like three Satie pieces" , "With hips very wide compared to the upper body" , "Bottom-heavy: (gone) wrong" .)