Once the middle is done, you can just hold each side one at a time in the hot water and shape it. I prefer starting by carefully pouring the hot water over the center of the mask while holding it over the sink. You can test it and reheat it till it starts to allow the mask to bend. It doesn't have to be boiling, just hot enough to bend the mask. If you use this method, I recommend heating up a big glass measuring cup with water.
If you are using a heat gun or hair dryer, you can carefully hold it on the form and heat it up while forming it to the shape.
