Hi Dave,
This sounds an awful lot like an issue we've seen here on iPhones quite a few times. On the iPhone, if you neglect to take out the screws securing the screen to the chassis and then go about trying to remove the screen, you end up separating the screen's mounting frame from the screen itself.
It seems quite likely that's what's happened to your screen. In fact, there's even a caution about that on the iFixit screen replacement guide:
[quote]During the removal procedure, make sure to insert your opening picks in the right position to avoid separating the screen from its safety frame.[/quote]
If you take a look at this picture from the screen guide, you'll see the mounting frame on the screen, outlined in red.
[image|2835391]
Now if you keep that image in mind and look over on your phone itself, I'm pretty sure you'll find that frame still mounted on the chassis.
The fix here is fairly straight-forward; just go around the phone again using the same screen removal technique and take the frame off the chassis. At that point you should be all set to continue on with your screen replacement.
Best of luck with it; let us know how it goes!