Do you really mean start over, or load your previous save? There are several deadly traps in the game (mostly in act 1), some of which you will have advanced notice of, and some you will not.
The note with the lever combination started to give a warning (however vague) before it became unreadable.
If you are having problems spotting levers, etc, you can boost the gamma setting in the graphics options, and switch the darkness setting to 50.
There is a message when you reach the end of the demo (you are nearly half way through).
Kiya's BD demo
screenshot walkthrough/spoiler