I am not sure exactly what your beef is. You had insurance that would cover the bill but you wanted the NRA to come in and spend g-d knows how much money to defend you for free on an issue that had nothing to do with the NRA's purpose.
The NRA only gets involved in cases that will establish precedence and or have a potential for personal injustice affects 1) firearms ownership, 2) carrying/transporting firearms 3) self-defense, 4)hunting rights, 5) range retention. 6) import laws, 7) ammunition restrictions. In your case the issue was a civil fine which would be accessed due to supposed negligence, related to starting a fire on government land. None of the above issues were in play, it had no relevance to the NRA's purpose of defending firearms use and ownership rights.
You did not go retain a lawyer... you could have tried that. In cases over 20 dollars you can demand a trial by jury. You could have made them prove it was your round, prove in some way your actions were negligent....etc. Of course it would have cost you money. Why do you expect the NRA to cover it? In any case your congressman cleared it up for you. seems like a decent outcome.
Don't get me wrong, but if the NRA got involved in every little action that anyone who was a member thought they had been wronged in they would be broke in a year. Second if they had got involved it might have gotten the range closed. When you fight city hall, they sometimes do that just to let you know who is really the boss.