If you have mixed the proper amounts of part A and Part B then it should harden according to the time it states on the mixing and curing section in the instructions. I have found out that many people guesstamate the amounts instead of measuring them very carfully. I my self use a scale and mix according to weight. Now I understand that not everybody has a scale that may be avaiable to them, but if you measure according to the directions then all should be O.K. The makers of Expoxy have spent many hours figuring out the ratios of how to mix their product in order to get it to work . Don't second guess these people, they know what they are doing. If you need to remove some soft expoxy that has not cured right use Acetone on a cloth and wipe it off, turning the cloth as much as needed.
Just in case you want to know what type of scale I use. It is designed for gunpowder and is very, very accurite ( I also re-load ammo) I have used this scale on all types of epoxy type adhesives and never had a problem of any thing curing, hell I even measure JB weld with it and that stuff is almost fool proof.