Well I have a Certificate in Art and Design as well as a Bachelors degree in Creative Technologies (Game art). The degree was 2/3 game art and 1/3 game design/development.
I'm actually pretty shy about showing things I work on to be honest but yeah, I've done art for the past 4-5 years education-wise.
I always found rendering hard in Maya because there was so much to adjust and alter so I opted to use a specialty program for it. The other thing also is I was only rendering objects and props for the most part, if I wanted to do environments I would tend to use Unreal Engine to get my images where it's more like you are getting a screenshot than anything.
I mean you just started right?
It's good, I can honestly say I wouldn't have gotten to where you have when I was your age.
I would say keep working on it, it will come. Something that might also help is figuring exactly what you want to do;
Do you want to do more of the 3d modelling side of things?
Were you more interested in creating scenes with models and getting a full environment?
Did you mostly like setting up lights and doing effects?
I would say figure out what is the core of your passion and start there, it's really easy to get overwhelmed by how much there is to do in game art specifically.
EDIT: As for the grass and the sky dome, it really depends on how you have created them. If you can just take a screenshot of the setup I may have some ideas but it could be a multitude of reasons.