I just did the same thing. I added four more schools - Columbia, Temple, UPenn, UIC last week. I know that it's absurdly late, but there is still a small chance I can get in, so it's worth the money to me. I'm kicking myself that I didn't do it sooner. I originally applied in early August to four schools, but am now concerned that it was too few schools to apply to since I have only received interviews from two of them.