His body shape is a bit blobby - can you get some references from T-rex skeletons and try drawing a sketch just as a skeleton first? I know you are using someone's lineart but can't you change it?
Also, he looks like he is spewing popcorn
When his bottom jaw is closed, woudln't it have a massive overbite?
I leave it to other people to advise on whether something needs to be done about the pallete.