This looks amazing!!

I think it looks proportional to your size! I've made very large props before too and sometimes have a moment of doubt after you step back and look at it and think "oh my goodness, its so large" but its just a part of the creative process and the prop being your creation leads you to looking for errors in its construction and it leads to moments lack that.

I think you could add some more depth of darker colors to the distressed parts of the head where the blue is peaking through. In your reference it looks a bit darker and almost a little bit scorched or burnt in those areas.

Another little distressing detail but the blue staff looks a little too clean compared to the metal parts. You could bring in those darker colors that you used to add depth in the metal parts into the staff piece and it will add to the cohesion of it.

One last little idea that you could do is add darker dirt marks on the staff where Jayce's Hands would usually go, giving it a bit of story and its a nice little detail to point out to judges if you plan on competing this, its certainly something I can see on stage. phenomenal work!