Oh please don't remove the cat -- it just adds to the folk art feeling of your quilt top. If it were me, I'd do something simple like a piano key border, using the muted colors in your quilt top. Possibly make the keys a bit wider, like using 2.5 inch strips. It would nicely frame your lovely top, and you could make it 7 inches wide on each side, which will give you the size quilt you want.
EDITED: Should have read through the comments first as others had the same ideas! The fence idea is also wonderful...we quilters are a creative group.