The database of the demo installation is wiped on a regular basis (I think every 24h), so I am not surprised that you can't find your survey.
The demo server is just for a first try of Limesurvey. If you want to do more with it, you need to install it on a webserver or contract a Limesurvey hosting service like Limeservice.com.
Help us to help you!
Provide your LS version and where it is installed (own server, uni/employer, SaaS hosting, etc.).
Always provide a LSS file (not LSQ or LSG).
Note: I answer at this forum in my spare time, I'm not a LimeSurvey GmbH employee.
