Music Composers Unite!
This piece is very beautiful and very lush. I only have a few comments as this seems to be already finished.
1. In competitions it is very important to pay attention to the very fine details in the score layout and formatting. There are a couple of instances where the expressive text covers the solo euphonium line. Also, general convention says that is better that the written parts should not have more than one dynamic level difference from one another. For example, there are instances where the solo euphonium line is at mezzo forte, while the woodwinds are playing at piano. These are admittedly small details, but these small details matter when judges are looking at hundreds of scores very quickly. You should be mindful of extra rests that may seem excessive. Instead of having a whole rest occupy an empty measure, you have half rests and quarter rests. Just be on the lookout for instances like these when you make one last sweep through of your piece.
2.Here is one small musical consideration for your future pieces. It is effective to use long notes to accompany slower movements and styles like an elegy. However, if used too often, it can become boring and repetitive. You can activate the texture of your background material by using rhythms on the pitch you want to sustain or you could shorten the duration of the sustained pitches and leave rests in-between your chords. These are just a couple of ideas to consider in future.
I hope this helps and I wish you the best of luck in your competition. Great Piece.