Here are some tips for knitting swatches:
-cast on the number of stitches given for 4 inches, plus a little extra.
-Measure your stitches honestly.
-Stitch gauge is crucial.
-Row gauge is not.
-Always wash and dry your swatch as you would the garment.
-If you do not achieve accurate, gauge, keep swatching on different sized needles until you do.
Does that help?