I bought a 6 inch cake with butter cream icing from a store. I remove the fruits and smoothed out the icing. I colored my Wilton fondant with blue gel color and roll it and cover the cake. It started to have tiny cracks immediately. I put it in front of window air-conditioner for several hours and it stabilized. I put it in the box and keep it in fridge. It looks good in the fridge. on the birthday day, only 10 minutes after I remove it from fridge, the cover started sagging and melting to the point that we could not use the cake anymore. While making the fondant cover, I tried to make sure the cover thickness is 1/8 inch. I color the white fondant with gel color, do you think that's the reason? I used a lot of finely powdered sugar while rolling the fondant to remove stickiness. Any help is appreciated.