How do I return my iPhone 4 back to the way it was after I accidentally backed it up with my old iPod's information, and now all my contacts, messages, and photos are all gone?

So I went to plug my iPhone into my computer, automatically pulling up iTunes/iTunes Store. I notice that the computer isn't recognizing my iPhone, so I look at my phone and see that it is asking me if I want to trust this computer so I click yes. Then on the computer on iTunes it asks me if I want to save it as a new device (which I should've done) or save it as a previous device (and showed the names of other devices) and I picked the save as previous device under my old iPod, thinking that it would just save it and not mess with anything (mind you, I have never backed this iPhone up before)... So I wait for it to finish saving, and when it is I realize my phone looks nothing the same as it was when it was my iPhone a few minutes ago (except all the apps I hade downloaded unto the actual iPhone) and now looked like my old iPod. It deleted all of my contacts (except ones synced from Facebook), photos (but had all the photos from my old iPod), and deleted every message I had had with someone. I know I made a mistake, and I honestly don't know if this is something that can even be fixed... But I need to at least try.! So if someone could help, I would appreciate you a lot!