Toffee can be chewy for a few reasons. 1) It wasn't cooked long enough. Please use a thermometer to ensure it reaches the proper temperature. 2) Humidity - if there is a lot of moisture in the air the toffee will absorb it as it cools overnight and it will be chewy. Make sure to store it in a cool, dry place. 3) The chocolate didn't completely coat the top of the toffee. The chocolate creates a barrier between the toffee and the elements (like humidity) that contribute to chewy toffee. So be sure the entire top of the candy is coated.