In order to fix the puckered areas, I believe you would have to take out quite a bit of your quilting, especially if there is excess fabric in that area. If the puckered areas are near the edges, it will be much easier to take out a small area and requilt, pushing the excess fabric to the edge. Can you tell if the puckering has occurred because of excess fabric or that the fabric is shifted? Depending on the purpose of the quilt and how bad it is, it might be best to leave it and learn from the experience. When the quilt is washed, it might not be so noticeable.