The picture is very well done for your first, you deleted the sky with precision and effort, but the brightness and perspective is waaaaay off. You added a night sky to a mountain at day time. Also, space cannot be red and blue at the same time, only if the colours are very dull.
Here is my attempt to fix it:
http://puu.sh/725Pa/9100261428.png
Thats what I think it should look like, except a bit brighter...
But seriously, for something you consider beginner's work, it's actually very well done! I'm looking forward to seeing more of your future projects.