If you are, in fact, knitting one row and purling one row to get stockinette, you can add a ribbing to the edge to prevent that.
If you're working garter and the edge is smaller than the main part, you can try casting on with larger needles to make it less tight.
"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