Hi Rowanny,
I'm sorry that happened to you. It's a bit difficult for me to diagnose your issue, if it was a web browser play that you lost your save, it could be due to your browser cache being cleared or insufficient cache? I recommend playing the download version for a more stable experience if possible. If you can give me more details I might be able to better investigate. Good luck!
Ah I can also recommend exporting saves to a download (using the three line options in the upper left corner) and importing those as a safer option in case your cache or cookies are cleared ? You can export saves and it will download a zip file that you can import saves just select the zip file again using the three line menu in the upper left corner of the browser.