If you're using the same yarn and needle, are you holding it single strand or double? There's no gauge given, but you should be getting something like 2 sts per inch with the yarn doubled. If every block has 12 sts then 9 blocks across would be about 108 sts and that would be close to 56". If you have more stitches per inch, then you need to keep increasing and do more blocks until you get the size you want.
sue- knitting heretic