Uncompressing your zip and opening the caproj raised a check failure that I ignored, and previewing the project launched JS assertion in my FF.
Last time I saw this, the person who was sharing the project had saved different projects under the same .caproj name in the same folder.
This is not really good practice.
As this is only a starting project, i'd recommand you to make a new project, and save as single file for a while (capx).
You can find more about it in the manual entry about saving and sharing projects and also have a look at the best practices for C2.
For now, start over from scratch, add a (little) sprite and set solid behavior to it.
It should stay in position and all should work well.
example capx (make sure to check the example capx in the folder C2\examples too)
Also you may want to follow such tutorials as How to make a platform game or Building a platform game