You can take a short-cut in this action by first doing a 180 degrees rotation, merge, then a 90 deg. rotation and merge, then a 45degrees and so on, until you have refined the pattern to what you want. You might need to attach a filled other layer to the layer with the line, to make sure it rotates around the middle of the circle, instead of its own middle (by clicking in front of the layers and a little chain symbol appears). I would use Illustrator for this (that can do step-and-repeat), but if you do not have that luxury then I think this is the best solution.