2" is big! That was with a diamond hole saw or carbide?
One of the difficult parts about redrilling will be keeping it cool. Maybe you could tape off the back side well so the hole would hold water while you drill? I don't know - just tossing out ideas. Another difficulty in terms of redrilling is being so close to the edge. I can almost guarantee that the vibrations of redrilling within 1/4" of the existing hole is going to make things much worse and possibly cause a serious crack. Personally, I would not redrill.
I noticed that you are going to be putting an overflow box around it. I would patch it (what can I say, I'm a cheap skate). Buy a piece of glass, say, 1/4" thick x 10" tall by 4" wide (as wide as it can be). Drill it then put it over that hole using silicone hiding the patch inside the overflow box. I would install the overflow panes at the same time so all the silicone cures at once. If the tank had actually cracked while you were drilling I wouldn't give the same recommendation.
If you don't get input here that makes you comfortable I would contact the Wet Web Media crew and ask them for their advice.