You got in! Congratulations! Only the real one knows that 

the moment the password is said out loud or shown to other people/players then just you, it becomes invalid

Anyways, you grab Trevor and return with him to Neville.

As a thank you, he gives you a piece of parchment paper and runs away down the corridor.

Staring at the parchment paper, you realize it is the

Marauder's map

Thankfully you heard of it before, so without hesitation you pull out your wand and say

"I solemnly swear that I'm up to no good"