Narcissists often feel deeply insecure, often to the point of thinking they are actually worthless and hollow. It's part of the emotional core that motivates their drive to appear perfect. They have no inner solidity, no firm sense of self worth independent of other people, so whenever someone thinks less of them they feel threatened and driven to attack. It's possible to be a narcissist and still feel worry that you might be a narcissist, as this is consistent with the general lack of a secure self image, and also because that worry is essential a selfish one. If you were worried about hurting others that might suggest not being a narcissist, but worrying only about your self and your image is consistent with narcissism.