Are you doing it in stockinette? Curling stockinette is just the nature of the beast and a very common problem. To combat the curling you could do an edge design on it like garter stitch or some other pattern. If you are too far into it to start over you might be able to pick up stitches to add the pattern when it's done.
There is a thread at the top of this forum that has lots of info.
When asking questions ALWAYS post the name and a link for the pattern if you have it.