Sorry, but unless you previously saved your work you cannot.
As for gimp freezing it's probably best to try and remember what you were doing at the time and report it. You say you have worked on files much bigger than this before but what was their size in MB /GB? Even a smaller x/y image can have a large size after being worked on. Best to save your work as an xcf occaisionally as it will save almost everything - then you will not have to start over if your gimp freezes and you have to shut it down/ or if you mistakenly close gimp.
As you found out - if your gimp ever freezes on you again you may have to close your computer down and start it up again to get gimp working as it should again
As for gimp freezing it's probably best to try and remember what you were doing at the time and report it. You say you have worked on files much bigger than this before but what was their size in MB /GB? Even a smaller x/y image can have a large size after being worked on. Best to save your work as an xcf occaisionally as it will save almost everything - then you will not have to start over if your gimp freezes and you have to shut it down/ or if you mistakenly close gimp.
As you found out - if your gimp ever freezes on you again you may have to close your computer down and start it up again to get gimp working as it should again
