Moved to the How do I section.
For reference pelinhanci questions like these are better off in the How do I section rather than Construct Creations - the latter is more for showing off what you've created rather than asking for help.
You might want to take a look at our Using 3D in Construct tutorial as it talks more about how the 3D features work, including collisions. The 3D features are still essentially 2D underneath, as explained in that tutorial.