Firebird, the amount of hardener is extremely temperature sensitive, and is also specific to the product you're using. For example, the can I have right now says for ambient 91F and higher 10 drops/oz, 71-90F 12 drops/oz, and 60-70 18 drops/oz. If you mixed it light and it didn't harden you've used up the reaction of the MEKP and no amount of heat is going to cause the required catalytic reaction at this point. Mix up a small batch, enough to put a light coat over the problem area, and go up to 50% higher on the MEKP than called for. The new layer will react with the surface of the old, sticky stuff and you should be OK, provided you didn't put it on too heavy.

I use a shot glass marked in fractional ounces for the raw resin, to be accurate on the hardener to resin needed, and pay strict attention to the temps.