That backup wouldn’t have different due dates than the due dates you have in your collection right now, so it wouldn’t change when the cards are/were due. Cards are scheduled to be due on “June 2” – not “3 days from now” or “3 days ago.” [The only thing you’d accomplish by restoring a backup would be to lose you any edits/updates/reviews you have done in the meantime.] Also, you’d still have to study all 800, so messing with clocks and backups doesn’t really help you.
Before jumping straight to the quick-fix-add-ons – I’d encourage you to read the rest of that thread, including my post that discusses why you should not use most of them – they will make things worse overall.
A better next step is just start studying again. Right now, you’ve only done a little bit of “damage” and only to the backlog cards. You can shift them out of the way so that you can get your due studying done on time, and work those 800 back in gradually. Here’s how I suggest doing that –