You probably applied too much too it, you dont need much, a tiny blob in the middle will get spread out when you mount the cooler, if you use too much it will act as an insulator and raise your temperatures.
As you keep running the system, the CPU keeps getting warmer because it can't power down to idle. It will continue to get warmer and warmer.
By the way, you won't get optimal temps from AS5 until you complete the 200+ hour curing time that AS5 requires. This is one of the reasons that AS5 is only a middle-of-the-road thermal compound nowadays, along with the fact that it's electrically conductive. The good stuff today requires no curing time at all.