Cotton quilting fabric should always be ironed with a hot, steamed iron before cutting. You should always unfold the fabric and iron in a single layer. Ironing your quilting fabric in a folded position can cause cutting problems. It is far better to iron your fabric well and then refold (do not press ). The selvages should be even and the fold at the bottom should not be buckled. You should hold your quilting fabric up rather then do this on a flat surface. If the bottom edge is not hanging straight, move one of the selvages in the opposite direction until the folded edge straightens. Sometimes quilting fabric is folded onto the bolt unevenly. If you do not fold your quilting fabric in this manner you can get a bow happening in your cut lengths. This becomes more of a problem if you are cutting border strips.
Once you are satisfied that the folded edge is straight, place your fabric down on a flat surface and take the folded edge and line it up evenly with the selvages. You now have 4 layers of fabric ready to cut. You need to trim the cutting edge before measuring. This is why it is always wise to purchase a little more fabric than you require.