If you want it to feel bigger, you have to give us some sort of reference to its size. Put something in the environment that we will recognize and we will have a better visual understanding of the scale.
Why don't you have a look at the Rift colossus contest winners? http://moonbeam13.deviantart.com/jou...ners-217179403
Especially the 1st winner. Not having a clue about how to display massive scale, I'd just try to observe what the artist has done. If you cover up the riders in the foreground, the colossus still looks massive.
You can look at the other entries too but there is a lot of rubbish on there with hundreds of +favs.
Atmospheric perspective seems to be one of the big things to get the effect you want. But even the details are important: right now, you have some fur there. With single strands. And because those stuff is really tiny in real life, it will make your beast look tiny, because you don't imagine those strands to be thick like trees, but still small as a single hair. Maybe, get rid of it. I have even no idea why a big creature living near a volcano should have long fur. It doesn't need that at all.
what also helps is if you try to deail the surroundings ...if a certain rock looks detailed yet small its more likely that he is quite big and thereby you give away that the actual size of the creature is even bigger ....or if you draw the underlying ground in a detailed fashion you are able to convey the same thing.