after a lot of problems obtaining a 2.5 mm thick surface, I finally got it. (https://forum.solidworks.com/thread/232368)
Unluckily, I discovered that my thick surface is empty, and that's not my desired aim.
How can I "fill" my thick suface?
(link to the file: https://drive.google.com/open?id=1snWZRXKDphH56NSrXWHUe-znASP8Ob5d )