I agree with several of the others that in order to fix the puckering on the back you would have to take out stitching and readjust the layers. It really depends on how bad it is. I have hand quilted for many years and in my younger days I used several hoops of various sizes and shapes but I always come back to my smaller ones because they are more comfortable to use. I think the comfort factor helps me keep my layers taught where I need them so I'm not wrangling the quilt for better positions. If it were me, I might leave it as is (if I were keeping it for myself that is). Nobody's perfect and I never produce a quilt without a flaw of some kind. It's all in what you can live with I guess. I bet when it's washed it will pucker nice all over and it will hardly even be noticeable.