The cookies are fine. This recipe calls for cooking on parchment paper. But parchment is a wonderful product. Parchment is a heavy paper. Parchment speeds cooking because you can quickly unload a cookie sheet coming out of the oven and replace it with a full sheet of uncooked cookie dough.
Many bakers swear by it.
You can buy parchment at specialty cooking stores and some supermarkets. This problem is increased when you have a big, flat metal sheet impeding the normal circulation of air. Turning a cookie sheet exposes the cookies to more even heat. If you don't turn the baking sheet partway through cooking, you may notice the cookies on the back corners of the sheet getting browner faster than those in the front middle. It should feel somewhat plastic, and be pliable without being too soft.