Incendiary air burst launcher challenge

I have been mainly playing medic. I am trying to finish all the medic challenges. I have the airbust and I have been using it ever since I got it. I am currently sitting at 981 damage out of 2000. This challenge is not tracking right. For multiple rounds I only used the launcher. I shot so many people ticking away damage. What I thought would apply to my launcher stat. Nope it added 8 damage. I started the round at 973 damage and after using it all game I made it to 981. I should have finished this challenge already. I like using the launcher. I would just like to finish this challenge. I am doing so much fire damage to people to see no progress.