Is it possible..u are folding ur fabric to cut ..and the fold is causing the small wave..or when u cut the cutting ruler is moving a little..I had this trouble at times..that is why I bought a slide lock ..it doesn't let the material move..or is it possible ..like we all do..u are picking ur quilt apart ..when it really isn't bad..unless u fight to get the piecing right as u sew..it really isn't bad..u will get it right..walk away..do something else..sleep on it..it will come to u..the only other thing I can say is..I don't pre wash either..I also do not use spray..I do iron..what needs to be iron..am carefully not pull ..so it stretches..if u put spray over the already seizing the companies use..since not pre wash..that makes for the possible stretch..good luck figuring it out