123D Design is not working on my iMac.

My iMac is a 64-bit dual core intel machine running OS X 10.7.5. I downloaded Autodesk 123D Design from the app store and it doesn not work. The 3D field is all distorted. Here is a link to my screenshot: http://heroestcg.com/3dsamples/Screen%20Shot%202015-04-17%20at%202.39.08%20PM.pn g I know it's free software, but I've really been hoping on getting it working on my iMac. Anyone seen this? Or is there a way to get an older version of 123D Design? Thanks.