I voted kepper because you could use it as a decent hole filler if you decide to complete the set. So kep it. It's not going to take up much space, anyway, right? I've kepped worse.
I'd need to see another 1-2 photos of the reverse to tell what it is - Not a die crack, not a plating blister (if it's the same '63 cent), and it's probably either a scratch, or possibly an occluded gas bubble, which occurs on copper cents, and can eventually lead to a lamination on the coin. How about a few more photos, closer up, better lighting?