How about purchasing an additional fabric that coordinates with the fabrics in the herringbone, plus additional white fabric, and create a single or double row of herringbone in that color all around the quilt? You could do the 4" border first and use this additional herringbone as a second border, or you could do the new herringbone as the initial border and end with the 4" border (or leave off the 4" border completely, depending on what size you get).
I think your stash fabric has too much green in it and the pattern is too regimented compared to the fabrics already in the quilt. I would choose a fabric that has more blue in it, and perhaps a "splashy" design, to coordinate with the existing fabrics.
Edit: What is the purpose of the quilt? If you leave it as is, it would be a good size for placing over the lap and legs for watching tv. If it is to be used to cover up on the couch for a nap, then it would need to be bigger.