Smooth Edges

Step 1: Control+Click on the layer with your pen tool shape to select it. Go to the channels window and press the save selection as channel button. This will create a new channel (called Alpha 1) with the selection of your shape.

Step 2: Press control+d to deselect the shape selection. Click on the newly created channel. You will see your shape as white and the background will be black. Now go to Filter > Blur > Gaussian Blur. The amount of blur may vary depending on how large your shape is (I used 6.0 for mine). You want to blur it enough so that the edges of the curves aren't jagged. Click OK once you are done.

Step 3: Press control+L to bring up the levels dialogue. You want to move the outside sliders towards the middle until your shape has nice and smooth edges. Click OK once you are done.

Step 4: Control+click your channel layer and then click your load channel as selection button. No go back to the layers window and create a new layer. Fill your new selection with whatever colour you want. You can delete the old shape layer, as you've got a new and improved smooth one.