Press and hold the alt/option key when booting your machine, and it should show your OS X partition. Boot into it, go into System Preferences/Startup Disk and select OS X to boot into it by default.
Press and hold "Alt/Option" key as soon as your here the "Bong" sound. Also, in Boot Camp options with in Windows, you can set again the default bootable OS as OSX. [During installing Windows, it defaults to Windows to allow easy initial install]