I haven't yet tried to make one, but I've heard from a friend that made one, that it is best to allow the bf or another friend to help out in the process of making one so they can help with the mix, and its best if there a person that you can mess around with to so they can like rub your balls, finger your ass etc, while your waiting for the mold to set up to keep your dick extremely hard, and also that a cock ring is also strongly recommended, just be sure its not a special one like leather or something as it will get in the way and will become covered in the plaster material.

Also I agree with the comments regarding not having enough material to complete the mold.