No one has mentioned using fork pins. I have always pressed to one side and nested the seams, but had problems with the slipping and not matching. I came across fork pins at a LQS and have been very pleased with the results. Fork pins are very fine and are like having two pins in one. Nest the seams and place one side of the pin on one side of the seam and the other side of the pin on the other side of the seam. You only have to pin once and no more slippage. These are one of my "can't do without" notions.