I put a red line inbetween each shot. For the farthest right line, you can see it is right next to that flag. So, to set up the second shot, id move the camera so that the right side is just at the end of the flag, but a bit more right. Then, place that layer under the first one, and move it left and right until its perfectly lined up. Repeat that same kind of process as many times as you want..you can even do a 360 degree panorama