Count every loop on the needle as a stitch. You have to 'attach' the yarn on the needle some way in order to 'cast on' according to the method, so that first loop is also a stitch. So if you need 20 sts, you put the first loop on, then count 19 more.
Many people claim the long tail CO 'makes a knit row' but it really doesn't. It may look like it as you're doing it because of the purl bumps, but after you do a few more rows, it doesn't quite look like the other ones. Most patterns do not count it as as row, but you may like one side of it better than the other after doing the first few rows. So just Cast on and after 11 rows, look to see which side you prefer and either do one more row or go to the next row of the pattern. If the blanket is one row less it won't matter.