Mac build clips screen edges despite resolutiuon selection

Hi, I'm building a game in-progress for someone else to play. I'm using 64bit Win7. I build for mac, and everything appears to go fine. When the mac build is run though, despite the resolution selected on the player, the screen horizontal edges are clipped severely. (say, 15% of the screen from each side is clipped out). It's the first time I'm attempting to make builds to run outside of untiy. I've had an initial look around and can't see any problems/answers that relate quite to this issue. Any help appreciated!