Considering your age, I thought the trumpet piece was excellent.
It has a rudimentary structure and emotional cadences, like a lot of the soft-rock ballads you hear on the radio, but is a really good example of that style of writing. Well done.
The other two were thrown together, as you say, each containing unexplored germs of ideas that could be expanded. You would do well to listen to lots of string and brass arrangements and try and begin to incorporate them into your ideas.
Your rhythmic sense is fine, but don't pour energy into something until you are sure you have at least one very strong melodic idea ( you knew you had it in the trumpet piece ! ).
I would be interested to know what instrument you play, and if you write 'on' it.