Always Butt Seam your Wadding

If it is necessary to join your wadding use the joining stitch most modern sewing machines have.  Cut the two edges to be joined as straight as possible, then butt them together under the foot of your machine.  Feed both sides through at the same rate making sure there’s no gap and the stitch will traverse the middle from side to side making a nice flat join.  Make sure you don’t allow the edges to overlap as this will cause a ridge in your top when it’s quilted.

Wadding, properly joined can be made up to any size without any detriment to the finished quilt, thus using up lots of scraps and no-one will know!