If the game is running slowly, the game probably won't reach 60 frames per second. Because the game engine with which the game was created regulates the speed via the frames per second. So if you played the game at 120 frames per second it would run twice as fast and at 30 frames only half as fast etc.
Or in short, your PC probably isn't powerful enough to play the game smoothly. Oh and one possible solution would be to use a more powerful PC to play the game.