Your Trapinch and Gulpin pictures are cute. They're probably not "professional-looking" enough so I doubt you'll get them (which is dumb), but I think they're pretty ace.
Particularly, they have a load of "story" which some curators praise more than others so. If you keep getting graded poorly-- by which I mean, not-catches, not that the Curators are doing a poor job-- I have something that I think it would be cool to see you try: Write a short little story-- sort of like you did The Trapinch and the Bug-- and then draw out the whole thing, like a kids' picture book.
Because I think that your drawings are like they are, pretty much just because that you like to draw. WinterVines mentioned that you your colouring is iffy (though he said it better). I think that's more the style of a kid who is enjoying him-or-her-self and not worrying about grades. Having used coloured pencils myself (who hasn't?) I know it can be a pain in the butt to fully colour and shade everything in solidly, mostly 'cause it wears down the soft pencil lead really fast.
So my suggestion for you-- not that I came in here looking to give you advice, or that my advice is actually any good-- is to keep doing what you're doing. Do try to improve, but don't push yourself so far that it makes drawing not-fun. Because you'll get "better". As your tastes change and your skills develop (through practice), you'll naturally get closer to what the curators on URPG are grading for. If you keep drawing, and keep enjoying it.
But yeah, just wanted to pop in and say I like those two of your pics.