Once you have cut the 45 degree angle off your strips, join them together so that the 45 degree angle stays true. You will need to sew from the angled end each time. This will give you a parallelogram shaped section as shown in diagram 2. (The straight edge may be on the left or the right side. Doesn’t matter which.) Don’t forget to press seams open.
Then you join the first and last strip together, making a tube. It will look a bit funny and out of shape at first. But once you lay it flat it looks like diagram 4. You can trim the uneven edge at this stage if you wish.
You cut the tube open (in a vertical direction, along the fold) with scissors (so as to cut just one layer) and then cut this long piece into 2 halves (same direction as first cut.)
Once you’ve done that, follow the instructions to cut 8 strips 6 1/2” wide across the stripes. (4 from each half.) Mix them up to get a layout you like, and join the 8 together, matching joins but keeping the top and bottom edges relatively level. (The top and bottom edges will be a bit uneven, don’t worry about that)
Trim straight across top and bottom, then add borders as shown.
Once you get the idea of making the tube, the rest is easy.