Am I putting my new lens on my DSLR wrong?

It is a Nikon D7200 camera, with a Sigma 70-200mm f/2.8 APO EX DG OS. Is this lens incompatible with my camera or am I just attaching the lens wrong? The lens looks too big for the camera body. Thanks!
Added (1). I feel silly now. It turns out the person who bought me the lens bought me one for a Canon camera!

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What are good lenses for the Nikon D3300. Telephoto lense and wide angle lens perferred?

What are good lenses for the Nikon D3300. Telephoto lense and wide angle lens perferred?

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Nikon Full Frame Obsolete?

With the introduction of the D500, is the D810 somewhat obsolete? The D7200 delivered DR and low light perf. Very close to the D810, and with the all new Expeed 5, is the D810 doomed? Maybe for certain landscape photographers, studio, etc, the D810 may be a better option, but for anyone else striving for best low light performance and other practical things besides that, AF, etc below D5 price on Nikon system, is full frame out of the picture? Thoughts?

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