If you have to heat it to melt, make sure it has cooled again. Repeat this and watch closely because soap will suddenly take consistency and must be poured into the mold. Cloth can then be peeled off and bars can be cut with a serrated knife or scored and broken. Age the soap for at least a month, unwrapped. It is better if it ages 2 or 3 months.
Failures sometimes occur.
Sometimes melting the soap on a very low heat and stirring it some more is all that is necessary to make it set. I mix the lye and milk. Then I put in the block of lard and stir until it has melted. I powder regular oatmeal in the blender. I add it some baking soda and glycerin to the mixture.