Your site makes me make an account before I can use it, whereas excalidraw.com doesn't, and also excalidraw.com seems to save my drawing just fine? I closed a tab and reopened it and my drawing was still there, presumably from localStorage.

The three-lines-menu also has a "Save to..." option that lets you create a sharable link or save to your local disk.

You can also embed the excalidraw drawing in the exported image. So you can drag/drop the exorted image back into excalidraw and edit it later.

I actually created a completely free chrome extension exactly for that reason helps you to save and open the files at excalidraw

https://github.com/AykutSarac/excalihub