It’s probably too late and I don’t see how you can save the file. Your only hope is to use Windows Explorer and move as much as you possibly can off the disk, let the machine sit for a while and see if Photoshop registers the additional space without a restart. Which I honestly doubt it will.

For the future - the scratch disk is not an abstract Photoshop setting. It’s real, physical disk space. When it runs out, the system freezes, and the fact that this happened shows you have so little that your whole machine may freeze up at any moment. Then you have much bigger problems than Photoshop or this single file.

As a rule of thumb, you should never allow your system drive to fill up beyond 70% or so.