Yes, you are doing something wrong. Choco Reflect works a vaccine; it prevents the symptoms from happening in the first place, but if you are already sick, then the vaccine is worthless. Using Choco Reflect after you're already hit with a debuff is just wasting the ability. You need to check what the next item box has in its cycle and determine whether or not to use the ability if the people behind you grab certain items. Lastly, Choco Reflect blocks Frenzied and Heavy, but it has no effect on attacks that are AOE.