COMPLETE newbie

OK. I looked through forums and blogs for a week before deciding to post my "issue" I am trying to learn how to mate this pad onto the cylinder in the orientation that I want. I made the pad as a part, and then added the part to the assembly(which was rendered using Compress) and may be the cause of my "problem"? When I try to mate to the shell concentrically it is offset from the shell, It won't attach to the shell? Also I can't do a coincidence mate? I'm assuming I haven't given Solidworks enough info to relate the mates to OR there are equations or something restraining me from getting the pad any closer to the shell? Thank you so very much for any input.