OS X Boot option missing

1. If you partitioned or choose the incorrect partition, it is larger issue.

2. If you are unable to choose OSX to boot from,

a. If BC Drivers are installed correctly and you have Bootcamp option in Control Panel -> System, please see Boot Camp: Set the default operating system.

b. If BC drivers are not installed, you can power-cycle and hold the Alt/Option key and see if OSX is an option to select.

c. Try the following,

Resetting the System Management Controller (SMC) on your Mac - Apple Support

How to Reset NVRAM on your Mac - Apple Support

Yes, please try 2c. If you go back to Windows, please download GPT Fdisk from http://sourceforge.net/projects/gptfdisk/ and run the following command from an Admin Command prompt. Run the binary from the folder where GPT Fdisk is located (most likely Downloads).

gdisk64.exe 0:

p

q

And post the output.

1. Start a Admin CMD window.

2. Type gdisk64.exe or gdisk32.exe after you change to the proper directory.

3. When prompted for a disk type "0:" without the quotes and press enter

Here are two screen shots should also help.