Do you mean that you're doing stockinette (knit one row, purl one row)?
It will curl unless you put on a border of some kind. Try knitting the first and last 5 rows and knitting the first and last 5 stitches of each row. This will give you a garter stitch border.
So one row will be all knit, and one row will be k5, p to last 5 st, k 5.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry