Originally Posted by
Fabaddict
chances are your cut edges are not perfectly lined up. Take your two selvage edges and put them together -- is the fold flat or ruffly? move the selvage edges until the fold is perfectly flat. Chances are your cut edge will need some straightening. Or, you can rip your fabric to get a straight edge. I don't like ripping, because I think it stretches the fabric, but it does give you the grain line.
I agree with Fabaddict! It sounded like a problem I used to have and it was because I assumed the fabric was "square" coming off the bolt. If you move the selvages as Fabaddict explained and then square up your fabric, it should help. Then fold your fabric carefully before you cut. This helped me a lot when someone explained it to me. That, and pressing, not ironing. Good luck, you will figure it out!