If I understand you correctly, you were downloading some porn and what you thought was going to be good viewing material turned out to be underage and you deleted it immediately? If that's the case that really is a raw deal as no one is perfect (although some cops go around acting like their shit doesn't stink and they're perfect and pure and when no one is looking they turn out to be the biggest criminals) and it doesn't seem like there was intent. Seems like you have a fighting chance but it is going to cost lots of money and it will be worth every penny. Maybe you and a good lawyer could get your own expert to so it was downloaded then deleted immediately once you discovered it wasn't what you were looking for and let that and lack of intent be your criminal defense.

Good luck.