1. Fold the bag in half, right sides together so that the cast on and bind off edges form the top of the bag. You will join together the parallel long edges of the bag using a crochet hook. 

2. Using a 1 yard length of the same yarn that you used to knit the bag, make a slip knot on the hook. Leave a 6 inch tail of yarn.

3. Insert your crochet hook under the loops of the first edge stitch on the front side, at the corner with the top edge of the bag.  Then insert the hook through the first edge stitch on the back side. 

4.  Wrap the yarn around the hook, then draw the hook back through the two edge stitches. You now have two stitches on the hook.

5.  Wrap the yarn around the hook and draw it through both stitches on the hook.  You have just one stitch on the hook now. 

Continue joining the front and back edges of the bag, repeat steps 3 - 5 along the length of the bag. When you reach the bottom of the bag, where the knitted fabric is folded in half, draw the remaining yarn all the way through the final stitch to secure it.

Weave in your ends using a tapestry needle or your crochet hook.

Repeat for the second side of the bag.