TL;DR -- The chances of recovering your demo are slim to none. If this was on an SSD with TRIM enabled the chances are practically non-existent.
File Systems on modern day computers use logical relationships for us Humans to find and organize data. The computer does not actually have a c:\Anything\sort\of\file.fileextension. What it has is a table that says the data referred to by this path name can be found at a specified physical location on the drive.
What this means for you is that using the same name as the previous file did not likely overwrite the file immediately. The down side to this is that you have left the computer on and presumably been browsing the web to look for ways to recover the data.
What you really wanted to do was shut the system off as quickly as possible. This would stop the operating system and any other application from writing files to the disk that could overwrite the data. Secondly if I am correct about browsing the web to find a solution on the affected drive.. if it is where your browser has its cache you likely have downloaded thousands of little files that all also have a chance to have over written that spot of data on your hard drive.
If you still want to try and recover it do a quick google search for something like Deleted File Recovery. There are quite a few software packages out there, mostly requiring a linux boot up or the like, that will look for the deleted file names and let you recover some of the partial data.
Just be aware the longer you are using your computer and the more you do with it the greater the chance the data will be partially or completely overwritten.