Lost HDD Space After Failed Boot Camp Partition And Safe Boot

Hi,

I tried to install Windows 8.1 on my mid-2010 15" MBP running 10.10.5, assigning 70GB to Windows. It took 3 hours for the partition process to reach 2/3 of the bar, before claiming it was unable to partition my drive. I tried quitting and restarting the process, but the partition still didn't succeed.

I thought I needed to repair the disk directory to make my Mac run faster again. I went into Safe Boot to repair the directory. After rebooting, and another try at partitioning, I notice 70GB of free space vanished from my system.

I have tried googling solutions to this problem. However, they are all from a few years ago. I tried booting into Single User mode to run the -fy check, but that wasn't useful.

How can I recover this lost space? Would I really have to purchase an external HDD to back up my Mac, and erase my Mac's HDD?

Thank you in advance.