Sewing Together the Boxing

We used seam tape.

We sewed exactly at 1/2".  We have a 1/2" guide on our sewing machine.

Because we used a rotary cutter and not scissors, our cuts on the fabric were very exact.  That allowed us to easily position and tape the sides together.  We only had to make sure the edges were flush against each other.

Remember that the outsides of all fabric are almost always placed together, and you sew on the insides of the fabric.  Then, the fabric is turned outside-in to provide a nice looking cushion.