No, you should not have any extra stitches other than what you count. I can only think of three points to make. Be sure you're counting all the loops of your cast-on that are sitting on your needle, including the slip knot. Make sure that when you turn and start to knit your first row, that you don't bring the yarn over the needle and create a yo. And if your first stitch is a purl, be sure you're not pulling up on the working yarn, which would reveal two strands of the stitch belonging to the last cast on stitch, effectively creating an extra stitch if you knit them both.