Well you can use 13 blocks if you really want to. One in the centre with border(s) on all sides totallyng half the finished size of your blocks and the 12 remaining blocks will fit around you central one - like a medallion quilt.
Or arrange the blocks in rows of 4 blocks, 5 blocks, 4 blocks - maybe on point if the block designs suit.
But if you want to add it to the backing, the easiest way would be to turn under your seam allowance and applique it in place (by machine or by hand). If it has a light coloured background or pieces you can use it as the label. If you add the block to the backing before quilting, it will be quilted through. I like to have my larger labels quilted through as it keeps them firmly attached to the quilt, but not everyone feels this way.
It's a bit hard to be specific without a little more info. How big are the blocks? Are they all pieced? How big-a quilt do you want to finish with?
BTW - the question is not bone-headed. 13 is an odd number to have to incorporate into a quilt.
Good luck whatever you decide. Hope we will see pictures.