Nice moon. I look at moons all day - I work for the Cassini imaging science team. Hmmm, which moon is that? Tethys? No not quite right... Rhea? Oh! Wait! It's EARTH'S MOON!! ;-)
Yeah, bad exposure, but workable. I had a go at enhancing this image in GIMP and put the result on my website along with some information.
Smaller aperture would be good - you had f/2.8, while
planets like to be photographed at f/8 or better, or not, depending. Cassini's NAC camera is about f/10-ish.
I've tried photographing (from Earth) the same phenomenon in the past, and it's hard to get a good exposure on a bright thing and a faint thing at the same time.
Next time (or last time if have a time travel machine) try taking two photos at different shutter speeds, one just right for the moon, and a longer exposure to catch the faint halo though it'll ruin the moon. A third image with an inbetween shutter speed, may be useful. There are ways to combine the images to get the best of each, the proof for which the margin of this blog is too small to contain!

Wow, thanks for taking the time to improve on my work! The ring was so vivid I couldn't resist taking the photo, but (as you mentioned) photographing bright objects alongside dim ones is tricky at best. Again, thanks for the advice. Next time I see something like that I'll know to play with the aperture settings a little more.