Sometimes it halps to pull the working yarn down and to the right before knitting the first stitch on a row. Then you can see that there is one stitch at the end of the left needle, not two. If you pull the working yarn up and over the needle, it'll look like two stitches.
You might try putting markers (a circle on contrasting yarn works) one stitch in from the ends. Then you'll easily be able to see if the extra stitches are coming from that pesky first stitch. Just slip the marker from one needle to the other, don't knit it.