How to sew on borders so that your quilt remains nice and flat.
Measure your quilt about 6" from the edge: top, bottom and middle. Take the average of this amount and cut your two borders this size.
Fold your border in half and then quarters to mark the fold lines. Repeat with your quilt. Pin the border to the quilt at these points and gently ease in the border evenly while sewing together.
Repeat these steps for the side borders.
If you do this then your borders should be nice and flat, not rippled. Rippled borders don't quilt flat but will have tucks and folds in them.
Using spray starch (Mary Ellen's Best Press unscented, or Faultless Starch) before you cut your fabrics will help to keep the grainlines in place. Then once you've pieced a block or section, press it again with the spray starch. This will help to keep your quilt nice and square and ready for the longarm.