GCSE Composition HELP! CALLING ALL COMPOSERS!

Percussion Composition FEEDBACK.mscz

So basically, I'm currently doing GCSE music.
Just completed my first of the two year course.
My composition was marked by my teacher, and came back as a C, 18/30.
The composition (musescore file) is attached, with red writing indicating feedback.
I find my teacher's feedback is difficult to understand and very vague.
So i've included all feedback and was wondering if any kind people would be able to take a look over it and maybe change it up a bit/kind of rewrite it?
It's a percussion study, with the percussionist playing Timpani/Vibes, hence why they can't cross over, and piano accompaniment.
Any help would be greatly appreciated.
I've also written my general feedback below, just so it's clear how I need to improve.
Thanks!

FEEDBACK STARTS HERE
A wide range of techniques for vibraphone/timps and piano accompaniment with some imaginative rhythmic ideas. However, there are perhaps too many ideas and the piece lacks economy of sections/development and clarity. Each section needs to be shorter, the melodic ideas need development and you need to show development in each section. I think you are trying too much.
HARMONY - Use of primary chords/relative minor in other sections, but ambiguous/unclear harmony in vibraphone minimalist section - this needs addressing. Opportunity to add harmony to timp solo.
TEXTURE - Homophonic/Monophonic textures/ some polyphony. Opportunity to mix instruments together, create imitation and more polyphony.
STRUCTURE - Clear ABCDA - but sections are VERY LONG and lack economy/unity/development - easy to fix!
PLAN/BRIEF - Clear plan. Detailed brief. Well edited score.
USE OF COMPOSITIONAL DEVICES - Detailed use of a range of compositional techniques but the devices need to be used in shorter, more compact sections - more impact!
STYLISITIC FEATURES - Perhaps too many different styles - too ambitious. Is it a study for perc instruments? (It is by the way!) A sonata? A minimalist piece?
TARGET SETTING -
1) Prune each section, do you need them all? ABACA is enough - rondo 16 bars each + return to A
2) Sort out the harmoy in each sction - range of keys/modulation
3) Aim for a length of around 3 mins - linking these ideas together but showing a range of techniques and a sense of unity
If you are writing a "study" for percussion, you want to demonstrate as many techniques as possible, but for GCSE they need to be relatively short - with clear melodies/motifs that you can develop
Finally, there are too many ideas - but you have the potential here to take a range of them and show real development and use of compositional techniques - try and find a balance between rhythmic effects, melodic ideas and a good range of chords and keys.
If you are going to do a minimalist vibe section, remember "Tubular Bells" create a strong melody and develop it gradually - and Steve Reich "Music for Mallet Instruments"
Thanks again.