The worst thing you could do (within reason) is to waste time in the audition, constantly bellyaching about the gear, and reminding the band that you're not used to this amp, whilst they have to endure listening to you playing the same riff over and over again, and fumble aimlessly with the EQ.
They should have everything setup, and ready when you arrive. So just double check the amp is warmed up, then plug in, set the gain, and play a couple of notes.
If it sounds ok, don't touch anything, and instead focus 100% on the audition.
If it sounds awful; bear in mind that the band may already have the amp set up how they want it to sound, so don't just march in and start fiddling.
Ask if it's ok to change the sound.
If they say yes, disengage any ultra low, ultra bright, and graphic EQ - you may also want to disengage the limiter.
Spend absolutely no more than 30 seconds tweaking the tone controls, and make sure you're not obnoxiously loud.
Get back to giving the audition your full attention.
You can always make further tweaks to the amp, between songs. Just limit yourself to 5 or 10 seconds at a time.
Style it out.
Good luck!