You might also be forgetting to move the yarn when you change stitches. To go from knit to purl you have to move the yarn from back to front, moving it in between the needles before doing the stitch. To go from purl to knit, you move the yarn from front to back in the same way.
Mommy to two wonderful girls
"I don't have to conform to the vagaries of time and space, I'm a loony!" -Campbell Bain (David Tennant) 'Takin' Over the Asylum'
OTN: Cabled Sweater
, arm warmers, kids' clothes