First time user, in need of help

I recently just tried to update the OS on my 2016 MacBook Pro 13” to the latest version using the video by SteampunkTV (will link in the comments). Everything seemed to have gone right and it’s updated but usually when updating, all the files remain on the desktop. After updating, everything is gone and my computer is pretty much factory reset, so my question for anyone that can help would be:

1.) did I lose all my files? If not, how do I get it back?

2.) on the screenshot provided, I feel like I missed a step and I’m worried I put the whole OS on my driver and not the internal hard drive, does that matter or I should be fine?

I mainly just want my files back tbh

Thanks!