As a trusted teacher, he was likely involved in protecting the Stone in other ways as well.
Snape seemed to be actively involved in protecting the Stone in ways other than the potions riddle. He went to check on the Stone when he got his leg mauled by Fluffy, which was left in the movie.
“Snape was holding his robes above his knees. One of his legs was bloody and mangled. Filch was handing Snape bandages.
‘Blasted thing,’ Snape was saying. ‘How are you supposed to keep your eyes on all three heads at once?” - Harry Potter and the Philosopher's Stone, Chapter 11 (Quidditch)
In addition, he could have helped plan the defenses, or given ideas to Dumbledore for how best to protect the Stone.
Even in the book, the potions riddle isn't the only thing he contributes to protect the Stone. He's suspicious of Quirrell, is told by Dumbledore to keep watching Quirrell:
“You see what you expect to see, Severus,’ said Dumbledore, without raising his eyes from a copy of Transfiguration Today. ‘Other teachers report that the boy is modest, likeable and reasonably talented. Personally, I find him an engaging child.’
Dumbledore turned a page, and said, without looking up, ‘Keep an eye on Quirrell, won’t you?” - Harry Potter and the Deathly Hallows, Chapter 33, (The Prince's Tale)
And confronted Quirrell about where his loyalties lie.
“… d-don’t know why you wanted t-t-to meet here of all p-places, Severus …’
‘Oh, I thought we’d keep this private,’ said Snape, his voice icy. ‘Students aren’t supposed to know about the Philosopher’s Stone, after all.’
Harry leant forward. Quirrell was mumbling something. Snape interrupted him.
‘Have you found out how to get past that beast of Hagrid’s yet?’
‘B-b-but Severus, I –’
‘You don’t want me as your enemy, Quirrell,’ said Snape, taking a step towards him.
‘I-I don-t know what you –’
‘You know perfectly well what I mean.’
“An owl hooted loudly and Harry nearly fell out of the tree. He steadied himself in time to hear Snape say, ‘– your little bit of hocus pocus. I’m waiting.’
‘B-but I d-d-don’t –’
‘Very well,’ Snape cut in. ‘We’ll have another little chat soon, when you’ve had time to think things over and decided where your loyalties lie.” - Harry Potter and the Philosopher's Stone, Chapter 13 (Nicolas Flamel)
In addition, he's the one sent to check on the Stone when his leg is mauled by Fluffy.