@newfarer, I'm a sales trainer and always addressing huge groups of people from all walks of life - nowadays I've become comfortable but it's been through years of doing various forms of public speaking since primary school.
Like sparkly has said, the moment you know your subject content, confidence becomes almost automatic but anxiety will always remain - however, the more you do it the more relaxed you become.
Have someone conduct an interview with you as if it's the true one - despite practicing, you have to learn to be able to speak off the cuff, this will be achieved through dry runs of the interview with a friend.
Muganda has also given you a very good pointer so try it, you've nothing to lose and everything to gain! Good luck
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