Fittonias are very good terrarium plants because they are small plants with small, fragile root systems and thrive in high humidity.
Unfortunately, the repotting into a larger pot has damaged the very fragile roots and that is what is causing the curling of the leaves. The repotting also makes proper watering extremely difficult.
I wish I had a solution for you, but given the fragility of this plant, all I can suggest is that you try to keep the soil around the roots barely damp. The misting is not an effective way to raise the humidity that it requires.
For future reference, keep your plants in their plastic nursery pots and insert those pots into something more attractive, but leave a plant's roots and soil undisturbed.