stockinette stitch confusion

[mockingbirdgirl.livejournal.com]

The incredibly long scarf I'm knitting in stockinette stitch is having a case of curling. The sides curl in on themselves to the point that I have a long narrow tube, with the purled side out. Is there something I can do now to rectify the problem? Or something I can do next time? Or at least, why does it do this???

Frustrated,
Elysia.