The issue that you're running in to is that, while you've changed your grid to a two column symmetric grid, you haven't changed your gutters in proportion. What Singularity is seeing with how you've currently set it up is that you've got a 2 column grid, each column is width 1, and a gutter of width 70. Now, there are two ways you can solve this. The first is to explicitly state what your sub grid is in relation to the main grid. That would look like the following:
#first-column {
@include grid-span(1, 1, 263px 263px);
}
#second-column {
@include grid-span(1, 2, 263px 263px);
}
or, with @include layout
@include layout(263px 263px) {
#first-column {
@include grid-span(1, 1);
}
#second-column {
@include grid-span(1, 2);
}
}
The second option is to set up the correct ratio for columns to gutters when using sub grids. Singularity works best when it's dealing with small ratios instead of large "absolute" values.
@include layout(2, (70px / 263px)) {
#first-column {
@include grid-span(1, 1);
}
#second-column {
@include grid-span(1, 2);
}
}
Hope this helps!