Fear not, it shall be awesome!
As for the jellyfish being too imposing, isn't that the point of a good villain?! ^^ But I feel like you should decide how important the jellyfish is, compared to the mech/creature(?) below. If the jelly is the real dominant character, maybe make it a bit more intertwined with the one below? And test out how it'll look if you extend the canvas so that it doesn't cut off the jelly's top (or rather bring the jelly a bit lower, so that the canvas doesn't get too long). I feel like it would feel better in the composition. Ok, I'm done rambling
Good luck, man! You can do it!