I used to measure my borders and pin and sew on until my LAQ and a quilter for 35 years told me to just make larger border strips, sew on and trim excess. I seem to sew pretty accurate 1/4 inch seams because I have not had any issues with wavy borders. I do wonder if it is the material difference between the quilt top and the borders though that could affect waviness. I tend to not mix Batiks and regular fabric and try to use the same-weight fabric throughout a quilt unless it is really scrappy.