Yeah, a panel of strangers staring at you from behind a table is kinda scary. O_o I think it makes it a lot more relaxed if the judges stand up too (if they can) so it's more like a real conversation - plus they can take a better look at the details you are pointing out then.
Some judges are new at judging, too - and they don't realize yet that they should give newer cosplayers some prompts, and might sit in silence waiting for the cosplayer to run the presentation. So, I do recommend asking the cosplay sign-up people what to expect and how to best prepare.
Taking a friend in with you for support (even if they didn't help make the costume and even if they are not entering themselves) should be totally fine, too, if it helps you feel more at ease.