He could hear her voice in his head. She was telling him that he had to mean it, that he had to want to cause pain for the spell to work.
But he didn't want to cause Ollivander pain. In fact, all Draco Malfoy wanted to do was find a way out of this situation without having to die. He had never realised what life as a Death Eater was like until he had been forced to be one, and given the hardest task to complete.
His aunt Bellatrix's voice slipped back into his head and told him to concentrate.