I have two GFG in progress. On one I am filling in the gap with 1/2 flowers and a consistent row of hexigons in the background color to end up with a fairly even edge. On the other I did solid rows of 9 flowers each and made a little cluster to fill in the 4 patch gap that created.
On both I filled in the side edges with the background color until I got to an even edging. I plan to cut the extra little 1/2 hexi's off after I quilt it and before I bind both.