If it's what I'm thinking of, you start with a stitch and then increase one stitch at the beginning of every row until you reach the right # of stitches and the decrease down in the same manner.
Not too long ago there was a similar post, but regarding a dishcloth. The poster had been increasing at both the beginning AND the end of every row, so the stitch count increased twice as fast as it was supposed to so when she reached the right number of stitches, only half of the rows had been completed (without realizing it) because the increases had been worked twice as often as they were supposed to. It ended up a very oblong shape rather than square. I wonder if this is your problem as well??