Packaged batting is always a bit bigger. If you want to add scraps, it is best to use batting from the same manufacturer. I use Hobbs. I cut a +2" strip of lightweight fusible interfacing. I overlap the pieces and cut with a rotary cutter. This creates a perfect match when the two pieces are butted together. I then fuse the seam with the strip of fusible. When I use to zig zag, I could feel where the sections were stitched thru the quilt. You won't be able to feel this seam. I do overkill and fuse the interfacing on both sides. Good Luck !!!