If you have neither a pen nor laser pointer, direct attention to things with an upward facing palm, never point. It shows more respect and doesnt intimidate people.

These are probably the best answers in the thread. Confidence is knowing that no matter what happens everything is going to be alright. So just keep the assessment in perspective. It's not a super big deal is it? Of course you want to do well but it's not the end of the world if you slip up.
Next, realise that most likely no one else really cares. Think about how you feel watching other people public speaking like that. Ask yourself how their performance was. Most likely you'll just answer "good". As long as you're calm and confident it won't matter if you make a mistake anyway.
I've mentioned confidence a few times now. Unfortunately for people trying to become more confident it's not something that can be switched on. But what you can do is maximise your confidence in performing your assessment.

2 ways I can think of immediately:
1. Practice the fuck out of it. If you know that you know the poem inside and out then you will feel confident. If you are unsure about some of the lines you won't feel confident. Stick it up in the shower, on the wall beside your bed, behind the toilet door. Learn it.
2. Have fun with it. If you can genuinely enjoy performing that poem then you'll either forget about any worries you had because you'll be so distracted having fun with the poem and/or you'll have so much fun with it that any slip ups won't even matter to you because you'll be enjoying yourself anyway. How you go about doing that is up to you though.

I'm sure it'll be fine and when it's over you'll wonder what the big deal was. Make sure to breathe and let us know how it goes when you're done.

Yeah, a simple way to remember this is the line, 'piss-poor preparation leads to piss-poor performance'.