Negative self-talk hits you when you're most vulnerable - like when you find yourself sitting in the reception area, waiting for your interview.

If you're feeling particularly anxious before your interview, try to clear your head and focus. Breathing deeply is one way to do it. Another is to focus on the sounds around you, and whenever you feel a negative thought pulling you back with its unloving arms, go back to focusing on the sounds nearest and farthest from you.
Becoming immune to anxiety in stressful situations is a skill. See what strategies work for you and practice.