Iron it well (all rows should go the same direction and then on the second tube the seams are ironed in the opposite direction;
This will help the butt up against each other when putting together.
Fold it at the center row and press that seam flat. We had 14 rows to ours.
Before you sew #1 strip to the last strip sewen make sure they are even; you may have to square the strip long ways first.
Then you lay it sideways and again make sure the ends of the tubes are squared before you cut your strips; about every 3rd or 4th cut check again to make sure it's squared so that it'll be easier to put together.