If that was mine I would probably recut the squares a little smaller to get rid of the serger sewing (rather than pick it out) and sew it on a regular machine with 1/4 seams and probably use some kind of stabilizer under the stretchy, perhaps tear away stabilizer with a little spray glue or Elmers to hold it temporarily (?). You will figure it out and it will be nice. Quilting is a learning experience. Meaning what I do one way isn't necessarily how I do it the next. I figure out easier ways as I go along. Good luck and show us when you get finished!