Timing Chain Installation Question

I am attempting to install the top timing gear on to my new camshaft. I got it all lined up but am having an issue. I needed a new woodruff key and ordered one but with the key way installed on the cam with the curved edge of the key facing into the cam groove key way and the flat edge on the outside every time I try to tap the sprocket on to the cam key the key will move and be at an angle. Is there any way to keep the key from moving so I can install the gear? I do not want to damage anything. Thanks.- maniac