I have never followed the idea of sewing strips in opposite directions and have not had any curve problem. However, I have seen multiple times where just sewing to another strip and then cutting it off results in one side being much longer than the other. You should always measure and then pin to ensure that one piece is not stretching out of shape.

Actually I like it and would use it as a design choice. Think of this as one large block, now make another when you have these large pieces completed then determine how to join them with sashing. You have a lot of design possibilities and most likely will have a significant wow factor. Good luck

Ive read this about 6 times and don't understand your instructions. All of this is sewn together. That's a large part of the problem. I think you may mean take it apart and actually measure things to be the same length. I thought I was so good I didn't have to do any of that:o

You understood correctly. It's the black that needs to go . . . .OFF! Then sew it back on after it is measured and cut to the same length. The colored strips can be eased in as you go. Use lots of pins if you need to.

Good luck!

Well....

at least it's consistent...? LOL

I DO like how it looks though, I like the ideas that involve keeping it as-is and working around it. You didn't screw up, you just invented a totally new technique!! :D

I would sandwich it, quilt it, bind it and hang it up as a great new innovation and a marvelous novelty eye catcher.

Another thing that may help: after the black is off, lay the colored strips on the ironing board so that they are straight. (Lay a long ruler next to them to be sure.) Then iron them in that position. If there seems to be a problem with curving, try a little spray starch. That should do it!

It is a feed dog thing. the feed dogs move the fabric, yes, but they move the bottom faster than the top.
Always use strips the same length and pinch the fabric strips between thumb and forefingers as you move along the seam, keeping the top fabric moving consistently with the bottom.

This is also why edges get ripply if a oversize length is just sewn to the edge and just whacked off at the bottom. And why borders don't fit when you know they should.

A good lesson that should serve you well for the rest of your quilting life.

Your end result just proved your last statement incorrect.....