wilnah,
I feel for you. Most of us have made serious mistake at one time or another and it's never a fun experience.
I hope the program Terry suggested works, but if it doesn't you need a backup plan for how you are going to recreate those records. Hopefully they were entered from some kind of paper input and they can be typed back in. Or maybe the users have printed reports from this data and you can recreate from that. Or maybe this data came from another data source and you can reimport it.
You also need to consider the politics of the situation and take the steps which will keep the screaming and blaming down to a minimum.
Since this a weekend, I presume you are the only one who knows about this? If your boss doesn't know about this, I suggest you call him at home before the end of the weekend and tell him. Note that I'm not saying you have to tell him immediately (although if he is a reasonable sort, I probably would). You can take some time to try Terry's suggested program first. Of course, the sooner you bite the bullet and tell him the less time you have to spend dreading it. Make sure you also tell him the steps you are taking to fix the problem.
He's still gonna be mad, but not nearly as mad as if he found out about it from the manager of the people who use this database first thing Monday morning. At least if you tell him before Monday, he can plan how he is going to deal with the affected managers whose employees use or enter the data and if you go to him with a plan, he can go to them with a plan. And it forestalls some of the blaming if you have already taken it on. Most managers truly would rather have an employee who is working like mad to fix a problem than one who hides it and they get blindsided when someone else complains.
Anyway good luck
Judy