There it is, that audition excerpt list staring back at you from your stand. You've been working through those orchestra fragments for weeks. However, something just might still be missing. It could well be that element in your playing that will make the committee want to advance you to semis. Suggestion: put the trumpet back into its case! For now it is not needed. Let's focus on just one thing.
Often the most deficient skill in auditions is steady rhythm. Good news, it should be the easiest to remedy. Most can play fairly well, but the beat is unsteady. Hence the audition committee shrugs and doubts that you can be trusted. You need not eliminate yourself for this reason. Instinctive rhythm should be a given. Of all things to miss on an audition, it should never be the tempo or the rhythm!
Start by clicking on the metronome obnoxiously loud with subdivisions if possible. Make sure you have a reasonable tempo for the excerpt. Don't be sent packing for your bizarre speeds. Internalize the beat and mark it by tapping with finger or pencil. Do this with absolute precision! With or without the metronome, you should be precise. Can you produce the tempo for each piece instantly without the metronome, and maintain it?
Next, you may add right hand fingers in exact sync with your metronome. Snap them on your left hand knuckles. That's why we have them, you know. Practice precision fingering at the right speed. Try this on the steering wheel while driving. Next, coordinate your fingers with your tongue. Tongue and fingers must be friends. Rhythmic perfection is your mission. Daily pulse out each piece with ever-growing confidence and insistence. Even slow excerpts must have a steady pulse. Be sure to subdivide to avoid rushing or dragging.
When you have absolutely had enough of this, then add singing with very exact pitches. This takes time and a lot of patience. If you can sing on pitch with precise fingering and tonguing, then you will have made huge progress! As you become more secure you can bring back the trumpet. Don't allow the horn to rob rob you of your rhythmic instincts and progress. You will find that a lot of style is achieved merely by great rhythm.