First of all, you made a really cute quilt for your Mom and I don't see any boo boo !! I would try an find a thread that will match the batik as close as possible. Make your quilt sandwich and quilt just inside the edge of the fabric. Take the stitching slow so you can guide your needle to hit the mark perfectly.
The background you might want to do something that looks like waves in the ocean using matching thread for the background. You want your turtles to be the star of this quilt. Your Mom is going to love it even if it is a bit late. Don't worry.