I've been looking around the Lion Brand site and I think you might be knitting this scarf
I notice it's a 1-skein scarf and I believe the seed stitch is intentional. While you can't tell the difference visually, garter stitch will produce a shorter scarf lengthwise than seed stitch. You can see this realy well if you grab some non-fuzzy yarn and knit a swatch of 20 stitches x 20 rows in each stitch pattern.
Garter stitch (knit every row) is quite wide compared to many other stitches but is very compressed legthwise.
Seed stitch has a similar width but more legth, probably close to twice as long.
if you have 2 skeins of yarn, it probably won't matter, but it's something to consider when choosing your stitch.