The best thing you can do it realise that it doesn't really matter. For one, if you have even a somewhat good seech prepared, and you manage to get most of your points accross, it is very hard to get less than a merit. You can definitly get a distinction even with a lot of stuttering and pauses, but the more confident you can appear the better.
However, my main point is this: imagine watching someone do terribly in their presentation; complete trainwreck. Would you care? How long would you even remember it for? Trust me when I say, your classmates will not care at all about your speech and will just be waiting to get theirs over with, and for this reason you should not feel worried about messing up.
Lastly, as long as you pass it (which i can guarantee you will if you deliver anything along the lines of a presentation), you actual grade will pretty much never be cared about be employers or universities.
Therefore, you should keep in mind that even if it feels like you're failing or 'blanking', its ok to stutter or take a pause, as noone actually cares and you will still get a decent grade.