Macbook Bottom Case Replacement

I recieved a MacBook (latest model 7,1) in October 2010, it was a birthday present from relatives in America (so is a US model), a few months after cracks started appearing in corners, by screws etc. so I took it to an Apple store to have it fixed, on recieving the fixed (new monitor enclosure and main body (due to unibody design had to be new British keyboard and trackpad)) I noticed that the bottom case had shifted to one side slightly, so I asked the Apple genius he knew why, he unscrewed if and tried moving but it wouldnt move, so I just accepted that I would have to live with it, however after a few weeks it was getting a bit annoying (I'm a bit obsessed with things like that), and we happened to be going to the Trafford center so I asked one of the people just walking round (I didnt have the MacBook with me at the time) what I could do about it, and he said that if I brought it to the store they might be able to replace it, however I never got round to doing it because our nearest Apple store is >1 hour away and I dont know of any of those Apple certified shops (not sure of their proper name) near where I live, but then I heard about this replacement program, so in my excitement I just went for the self service option without really reading anything, so I didn't know about melting glue problem (I wouldnt blame anyone for not believing this).

I have just recieved the email saying it's been dispatched, but I read that I have to return the old bottom case, but obviously the problem isn't the glue, so there is a problem, but not the problem they're looking for, so I don't know what to do, are Apple just going to think I was trying to get a free bottom case?

I've written an essay without noticing, sorry 🙂

Any help would be really appreciated, I'm sure Apple will be understanding as they usually are, but I doubt they will be happy with me.

Thanks

Ben