It's likely that the mistake happened with the yarn overs, especially if you're not used to doing lace knitting. How are you doing your yarn overs? Some get confused and think that a yarn over is a combination of bringing the yarn over the needle and knitting the next stitch. A yarn over is simply bringing the yarn over the right needle and immediately proceeding with the next instruction, whatever it might be.
If you're doing the yarn overs properly, then the only thing I can think to suggest is start over and make sure you count your stitches following every row. If your stitch count is off, then at least you know which row the error is occurring on.