When approaching the corners, only slip stitch 1 time over, for the actual corner, work the slip stitch into the same chain 1 space 2 times. Then, on the next pass, only slip stitch 1 time to the next stitch. You are trying to get the ribbing to fan around the corner.
On the last row of ribbing, tie off and cut yarn with a long tail. Use a tapestry needle to sew the last row to the first row joining the two ends together.
Weave in all ends and tie off.
Design by daisyfarmcrafts
The downloadable pattern is available here.