My guess is that you're knitting a stitch twice instead of once and slipping it onto your right needle. Its good to count your stitches after *every* row no matter how much experience you have, so you know that its only growing up and down and not side to side. If you're following the pattern for the envelope purse as best as you cna (im not so good with patterns
) and its still not shaping up, what I did was just knit a few squares in garter (knit) stitch to get the feel of the needles.
I hope this helps and please contact me if you have any questions! If i cant answer, im sure i'll find someone who can