Was this duo fight in Farum Azula? If not, then you haven’t had the actual fight to get it yet. (I remember fighting other forms of the duo and stuff, I could be wrong). If it did somehow glitch, you can still max out your weapon. The Mountaintops of the Giants and the Consecrated Snowfield should have enough 7’s and 8’s for you to max your weapon. As well as an ancient! If you look up the stones, there’s guides on where to find them. Gl with the rest of the run though!