Here's a corollary to the post I did the other day, Tip: Clip the Selvages Before Laying Out Your Pattern. Some knits have rolled edges that are knitted more tightly than the rest of the fabric. This can cause curving and tension at the edges, and can make life miserable when you try to lay out your pattern on them. Worse, if you don't do anything beforehand, it can cause a fair amount of distortion in your garment. Fortunately there's a really easy fix: trim the selvages. Here's a shot of a rayon jersey with the kind of selvage I described.
Note that the selvage pulls the fabric into a curve. To alleviate this, simply cut the selvage away close to the rolled edge. That will allow your fabric, and by extension your pattern, to lay flat for more accurate cutting.
I only trimmed about ½ inch from each side, so you really don't lose much fabric. It only takes a few minutes, and the results are totally worth it.
HTH, and Happy sewing!