It won’t effect how you keep them or your enjoyment of them but you don’t have Julii cats, very, very few are ever seen in the hobby because of the area they come from. You have C. trilineatus, which is much more readily available, often known as the three line cory or the false juli cat. Check out planetcatfish.com and you will see the slight differences from spotting to squiggling pattern.
No real differences in size or how you keep them but a lot more information available and easier to breed.
Would take the tetra back and get another “juli” in my opinion. They won’t bother the fighter and he shouldn’t bother them and you look to have a great setup for them.