The fabric is probably polyester. Cotton can take high heat from an iron, but polyester requires only a warm iron. Also it's best to iron polyester from the wrong side only, so as not to leave a shine on the right side.
Have you cut the fabric? Polyester frays more easily than cotton, so you may see many more strings along the cut edges. If the pattern you are using allows it, you might want to use 1/2-inch seam allowances instead of 1/4-inch.