Hey, thanks for trying the demo.
Well, you're not actually stuck down there but I know what you mean.
So if you are planning to continue playing this is what you have to do:
Start running from the previous room to the left and you should be able to run over the bridge.
This area has been completely changed in a newer version as this was causing issues for some players, so the bridge thing no longer exists.
Demo has not been updated yet as you now know since you played it.
I have plans of updating the demo at some point to better reflect the current state of the game.
Anyway, glad you like the game even with these issues. :)