That's unfortunate, I know how it feels. Best way to avoid that for the future is just to save more often, waiting 3 hours to save is a bit irresponsible with a big piece like this xD It's happened to me before, with just as many and more hours - I've learned to save frequently, like every few minutes or so
I know you can do it though! You've gotten this far already, maybe relax a bit and come back to it tomorrow?