I tried my 1st bargello and after cutting all the tubes I also was afraid to mix them up by mistake so made some straight pins with letters glued to them to help me keep them in order. Wasn't prepared for the price of the ready made ones plus didn't want to wait for an online order so made my own. Got some baby bracelet beads, slipped them onto straight pins with the yellow heads on them and used Elmer's non-washable glue..........finally found a use for that bottle I picked up by mistake. These pins have saved my bootie a number of times now. Made up 8 sets for a fraction of the cost of ready made pins.
I also heard about sewing one direction and then the opposite direction on the next row. I did that and didn't have any waves or bowing in my rows........so I guess that tip works.