Hello, first off I want to clarify I'm new to SolidWorks and 3D drafting in general

I've created a simple surface with the goal of making a cast. I attempted to part surface but it runs an error: "failed to create surface due to geometric condition." When I run the check it says: "Open Surface (1)." I know I'm supposed to add thickness to the surface but that runs an error as well: "face which failed check."

I've attached the file to make it easier to understand. If anyone can point me in the right direction, I would greatly appreciate it.

Thank You!