I did the Bartali log 10 that gives you a 100 failstack scroll today. I took the scroll quest from black spirit after, received the scroll and went on my way to fail at enhancing, business as usual. Then a bit later, I switched to my low level char that I'm leveling and noticed I had the 100 failstack scroll quest on my black spirit for a second time and I got another one. This obviously shouldn't happen. I checked my other chars, but it only appeared on that one character.

I don't want to get banned for duping or something, how do I fix this?

You're fine, you get two 100 stacks. One from Book 10 and one from Book 14, so enhance/fail away!

Haven't done anything past book 10 though, that's the thing.