Cant find my "windows" drive

Hi! I just bought my new iMac 21,5" with 1TB harddrive.

I just tried to install Windows with bootcamp and i used a USB with windows on it.

My computer has 1TB harddrive so i used like 499GB on each drive, when the boot was done windows told me to restart my computer because i need to take out the USB from the computer. So i did and when i started the computer OS X opened up again.. I opened up boot camp again and half of the drive was gone (only 499GB with mac) and the bootcamp only askes me to start a new installation of bootcamp. Ive tried to start the computer by pressing ALT and only the OS X system can be found on 499GB. HELP?! How do i atleast get my harddrive back... Haha