There could be a couple of reasons why the puff pastry didn't rise or puff. The pastry has to be cold, very cold. Puff pastry relies on the contrast between cold butter and hot water to create steam that pushes the layers of dough apart and makes the pastry rise. If the dough is too warm, the butter will melt which means the pastry will not rise when baked. The second common reason is the oven wasn't hot enough. Puff pastry needs to be baked in a very hot oven in order for the steam to create enough pressure to make the pastry rise. If the oven is not hot enough, the pastry will not rise properly. Preheat the oven for at least 15 minutes before baking the puff pastry.