Sometimes when there's several stitch patterns, or in lace, the gauge is supposed to be in stockinette stitch. They figure if you match that, the other sts will be okay too. So you don't quite have 5 sts per inch, try a smaller needle, and make sure you CO about 24 sts to get an accurate measurement. The edge sts shouldn't be included because they curl under and will be a little different size than the other sts.
sue- knitting heretic