I actually fail to see what exactly isn't symmetrical about it, I assure you it really is. The model itself is just a half that's mirrored. It has to be a mistake on pepakura's end. But I'll look at it when I get the chance to make sure.
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If you want to go right a head! I'll be 3D printing it in November when I get my 3D printer. But I'm sure everyone who doesn't have a 3D printer would be extremely grateful!