I was just looking at the pattern, and I found your extra 7 stitches:
Row 39: knitting every row decrease one stitch each side of row until you have 7 stitches leave on needle to start cuff.
Be sure that back of slipper is facing you. If not knit another row.
Change color if you want cuff to be a different color
Cuff: pick up 10(12, 13) stitches along side, than 13(15, 18) on top, 10 (12, 13) down the other side.
So you've got 7 stitches on the needle from row 39, then you pick up 13, 18, 13 on the cuff row --- which gives you a total of 51.
Then you purl one row, and knit 9 more, then pick up the 51 stitches on the purl row and bind them together using that 3 needle bind off that Kelly mentioned.
Hope that helps!!