Welcome from Ninnie in NC

It could be either, If stitch is too small it will pucker and if tension is off it will pucker.

Welcome from one newbie to another! Your stitching problem sounds more like the tension is too tight. When you sew other things, does it do the same thing? You might try stitching and adjusting first your stitch length (the easiest adjustment!) and then your tension on something other than your quilt until it is like you want it--could save some wear and tear on your quilt and yourself. You don't want to have to take the stitching out too many times!

Welcome from Southern California