A Canon EF-S 17-55 IS USM would be better. But not cheap, although if you are getting paid you should be using the best. I have not been to a boxing match live, but I guess they will be well lit, so that's something in your favour.
Being ring side is not necessarily the best place to be I wouldn't have thought. You will need to be constantly adjusting the focal length and focus as the action draws near or far away.
I would definitely try and get down there to test my intended equipment during a practice session.
Graham