just bought watch dogs for my mac and i installed it but it wont let me play because it says that i require directx 11 and when i go on dxdiag it says that i have directx 11

Most likely as the MBP 8,1 has only the built in graphics chip which will only support the simpler games. You need a lot more graphics capability.

Had the same problem on my iMac running bootcamp Winows 7, a thread recommended updating to Internet Explorer 1, as a working version of DirectX11 is bundled with it, this did not work for me, but made me think to update to Windows 8.1, which enabled by iMac to run it