If the cookie dough is a little bit sticky, then leave it in the fridge for 10 more minutes to rest. That helps the butter to get colder and then it will be easier to shape the cookies. However, if the dough is too sticky and there is a significant amount staying on your fingers when handling it, then you will need to add more flour. To avoid the dough getting too hard, I recommend adding just one handful at a time, incorporating it and checking if you have reached the desired texture.