You should use "ignorant", then. One of the more dominate

meanings of "innocent" is
" -- free from legal or specific wrong;; guiltless."

So, you are not "innocent", even if you can successfully argue that you "did it without knowing". (Another speeding ticket I got is because the highway I switched to has much lower speed limit. It was the first time I drove in that state. :-O)

BTW, if you got your two school zone speeding tickets in the same school zone, you cannot claim ignorant, either.

Still, please be more careful when driving in the future; at least for the sake of setting up a good role model to your kids.