There's a trick to sewing long strips of fabric so they match from
beginning to end. I saw this on Youtube but can't find it.
Hope I can explain this.
You line your two strips together, put them under the presser foot, then
fold the strips partway (about 8-10 inches) hold on to the strips that way
(like you don't want to sew further than that point), sew those 8-10 inches
then stop and fold the fabric again and sew the next 8-10 inches, etc.
Clear as mud? That's how they sew on industrial machines.
If someone knows the video I'm talking about, please post the link.