eliminating gutters

nav.scss

nav {
  float: left;
  width: columns(4) + gutter()*.5; // the outer two just need half a gutter added.
  &:nth-child(2) { width: columns(4) + gutter(); } // the middle needs a full gutter (half on each side).
  @include nth-omega(3); // you might not need this, but it may help keep things clean.
}