In general, you need to make sure that your score is easy to read, is consistent, and correctly communicates the musical ideas from your brain to the people who will actually play the piece.
With this in mind, I have a few comments.
Something is fishy with your transposing instruments. If I read correctly, you're in concert C Major. So, your trumpet/cornet should be in D major, your french horn should be in G Major, and your clarinet should be in D or Eb (depending on whether it's Bb or A). Unless there's some display issue with the online viewer?
On that note, there seems to be loads of pages with just one or two bars. This would be quite annoying for a conductor. Again, it could be an artifact of the online viewer? If not, you need to format your score so that much more of it fits on a single page.
I'll second the call for rehearsal marks. I prefer bar numbers to letters, but either is better than none. I'd also recommend that you change the name of the instrument at the start of the score so that it's really clear what you want. You should replace "Violins, Violin I" with "Violin I", for example. If you really want clarinets in A and Bb, they should be two separate instruments. My guess is that you'll be happy with just the Bb clarinet. Do you really want a contrabassoon?
Musically, be aware that you've written the flutes quite low. This could be intentional; it's perfectly playable, just a touch unusual. There are also some quite wide leaps in the woodwinds. Probably playable, although you may raise an eyebrow or two. Also, you have staccato crotchets in the cellos, and simultaneous unmarked crotchets in the violas. Is this intentional? You also haven't used all the instruments in a standard orchestra (e.g. trombones). Will this meet the requirements for your competition?
There are probably other things I could raise, but that's a start. I hope it is helpful.