Slip stitch edging is only on one side

[AnnaT]

Hi,

I cast on for the Besotted Scarf today. (I needed a break from my st st sweater) I am slipping the first stitch of every row and knitting the last stitch as the pattern says. But the pretty chain is only on one edge. The other edge looks like garter stitch edging. I wanted to have the nice chain edge on both sides. What am I doing wrong? I am slipping the first stitch knitwise.

Thanks!