I recently had a similar problem to you, Karen, except as a new user I hadn't thought to back up my projects. I managed to create multiple duplicate individuals (40 odd in some cases, all with exactly the same data).
Well, I've started group merging, but this just leaves me with millions of events to delete, so I guess I'll have to start data entry again (I'm just glad that this is my initial family data, no further back than Great-Great-Great-Grandparents).
What I would like some advice on, is how to avoid this happening in the future. Are these mutliple duplicates etc. etc. due to my trying to merge two projects (several times, because it didn't appear to work - if anyboy's got any tips on that aswell I'd be grateful)? I'm a bit worried about starting again because I'm afraid the same thing will happen and my tree had degenerated into 3000 people's worth of chaos just within four generations.
I would really appreciate some advice as to what I possibly did wrong, and the best way to start again.