Scarf curling in on itself...

[SanFranciscan]

I just finished my first scarf (woo-hoo!) and I'm so happy. The only problem is that it keeps curling in on itself. In other words, if you hold the scarf lengthwise, the edges roll in until it's almost circular.

I'm guessing this is because my stitch is too tight, but is there any way to fix this problem after the project is done? I've already cast-off.

Thanks in advance!