Sugarfun - how wide is your border? Generally, I find you need about a 6-stitch garter border to keep things from curling. Even then, a you'll have a little bit of curling with a piece that is pure stockinette stitch. If you want a stockinette scarf (which is nice and smooth) that doesn't curl, try knitting a double-weight scarf, either in the round (get a short circular needle) or knit double wide and sews in half.
U.S. 11 needles, 25 stitches, 2 st border for each side. Total 4 st. It 4 ply yarn, acrylic and cotton(bi-color)(tan-black-tan-black,etc) I may sew in half depending how wide it is finshed.