Yes that was zigzag. I never had this problem with my old machine, used to be straight as a board on the back. It was so bad to me that I ripped it all out and re-did it in straight stitch. It still has "waves" like that but not quite as bad. And yes I usually reverse direction when I am sewing in lines which is what it making the ripples change direction.
I basted the same as usual, by taping the fabric to the floor and then pinning no more than a hand-span apart. This has always worked fine for me in the past.
I already decreased the pressure on the foot from the recommended 5 to a 3.
I've got another runner ready to go and I'm kinda scared of messing it all up
