Possible Clues:

• It's wrong to have taken the head off
• Mistake-making
• Blundering
• Perfectionist's dread
• So having got its head off is 7 down for a fish
• Being off target
• It's wrong for the fish to have had its head cut off
• What the cockney girl has on hand is not the right one
• You'd be wrong to cut off the head of the fish
• It's wrong to be cutting the head off the fish