Well, you can always sight read the lyrical stuff in the Arban book.  

  It`s always a good idea to shake hands with your judges.  Be friendly.  As for scales, obviously, a B flat trumpet only has a range of 2 and 1/2 octaves, so the only ones i would attempt at 2 octaves would be F sharp through C.  As for your chromatic, just play the entirity of your comfortable range.  Hope this helps.  And nerves only make auditions worse.  good luck.  
