When I did a PS quilt, I did it in columns. I joined 40, 2.5" squares into a long row. Whenever I'd get a free moment, I'd add a few squares. I'd have long strips about 80" long. When I had enough strips, I laid them on my design board and changed around the strips until I was pleased with it. Then I pressed the strips...alternating the pressing...press strip up, next strip down and so on. Then I joined the strips, nesting the seams.
Worked great.
One caution.......be extra careful pressing the strips, or they may warp.
Good luck.