First, the bind-offs should have been at the beginning of each of 4 rows, so that you have removed 4 stitches from each side. The decreases wouldn't have only been on the knit side, but on the purl sides, as well. If they are not even, you'll need to go back and correct this in order to have the sides even.
Once you're set with the above, decrease at each edge on the next row (ssk, work to last two stitches, k2tog).
How often you do this depends on the size you're making. If you're making the smallest size, do this decrease on every 4th row after this.
If you're making one of the larger sizes, then do the decrease every other row.
Work until you have the number of remaining stitches for your size.