I'll explain some things so that you have some peace of mind, not because I feel like excusing the demo. The demo is a sliced off part of the whole of the full game which is one continuous process with nearly no hard blocks. The demo is not a good demo, but it's a great introduction to the entirety of the game. I've accepted that and I prefer it that way. You successfully progressed past this section of the game and were allowed to continue. The issue of players sticking around the grounds too long only exists in the demo, and it's because some players want to try as hard as they can to 100% the demo, which was never intended to be the experience and it's why there's several warnings throughout the demo that give you an out. It's possible, but like it's said in the beginning, it's more difficult than it should be. That warning is there for a reason, because I know what tends to happen, and the game is designed to discourage brute forcing.
There are 20+ progress triggers around the grounds. After only 7 the museum can be 'entered'. If you imagine you're playing the full game there is no mandatory wandering around the grounds for 2 hours (unless the player really really wants to) and this is the point where the game hits you with 5 more puzzles in rapid succession, making it clear that puzzles are almost never immediately solvable.
I'm assuming you unlocked both sections and I'm assuming you know that they get marked red when you have the info to solve them. Different clues are differently difficult to find. The cotton is not supposed to be easy to find. Some case pieces appear in multiple places for a reason. There's dialogue that nudges the player to end the demo if you have found enough things. I believe in free wins but I don't believe in making the demo unnecessarily easy to guarantee as many players as possible just accidentally solving everything solvable. I wouldn't play a game like that and would feel like it's playing itself and treating the player like he's dumb.