I would suggest making a 64x64 version, replacing your previous work's 100x100 preview image with that, and then setting it as your avatar. It's not actually necessary to post the avatar version as a completely separate gallery submission.
This was only for my avatar, a 48x48 version of the Fire Wisp.
You already submitted the Fire Wisp so this is not a valid piece for the gallery.
I will try to make a new avatar anytime soon.