Okay, I need some help...
I've got a digital camera (Canon Rebel)and I bought a 300mm telephoto lens for it (made by Sigma). Trying to take some photos of local neighborhood birdlife in my backyard. What I see through the viewfinder is an upclose view of what I would hope would be what I capture when I press the shutter button. But for some reason, the captured image appears as if I were still using the default lens instead of the telephoto lens. There's a little switch on the side of the new lens that can be placed in two positions "normal" and "macro". I've tried them both but get the same result.

The links show a picture of approximately what I see through
viewfinder (only much more detailed and sharper) but the next one is what I wind up with.

Can someone please tell me what I'm doing wrong? Is there something wrong with the lens or the camera?

first pic link:
http://www.geocities.com/ericdriver/bjay.jpg

second pic link:
http://www.geocities.com/ericdriver/bigblue.jpg