Neville's "Standing up to his friends" not nearly as strong as it is in the books for 2 reasons
When the Trio are leaving to deal with Snape and Neville's in the common room trying to stop them. Well it's not nearly as strong as it is in the books for the following two reasons
1)There's no almost midnight duel with Malfoy which in the books is when the Trio (before they become the Trio) and Neville discover Fluffy. (Not to mention Hermione's "I'm going to bed before you come up with another clever idea to get us killed or worse expelled" comment AFTER dealing with the troll in the movie makes no sense at all that's comment makes more sense pre-troll)
2)Since they replaced Neville with Ron in the forest-Neville doesn't get caught up with the dragon business (not to mention Ron doesn't write to his brother Charlie about getting the dragon out). And they lost many points because of the dragon shit except only Hermione, Harry know it's true. Ron was in the hospital wing
So because of those 2 things- how would Neville know that the Trio was "going out again" when they hadn't been out-except for the one time to see Hagrid?