I had to go wayyy back in my save states, train all the way, grab the horn for extra power, and when you train in the sewers click crush. I think also if you talk with Ella you get strength up to 81. that's how I fixed it.
ok, I try again the battle, here is what I choose, first I choose the eyes in shopkeeper, and when Valvaran charge his blade, I choose stay away, and after that, I choose go all out for it, and don't need evolve, then I win. If my choose doesn't help, I am truly sorry(my power is 65 and my skill is 17)