Placed prepared mango in a bowl. Add sugar and mixing well. Let stand for 10 minutes, stirring occasionally. In small bowl, stir the pectin into the lemon juice. Add pectin mixture to the prepared fruit, stirring constantly for 3 minutes, until the sugar is completely dissolved and no longer grainy. (A few sugar crystals may remain.) Pour and seal the jam into well-washed and dried 1- or 2-cup capacity plastic containers with tight-fitting lids, leaving 1/2-inch head space for expansion during freezing.
Let the containers of jam stand at room temperature for 24 hours until set, then freeze.
Note: To acquire 3 cups of prepared mango you'll need 4-5, depending on size, ripe mangos. Peel, pit and cube them. Place in a food processor or blender and pulse to a very fine chop, not a puree.