Ubuntu installed on flash drive - Don't want to accidentally wipe entire mac HDD

Good afternoon,
I have recently signed up for a linux class at my university and have decided to install ubuntu onto a jumpdrive to run on my mac. I have installed 14.4 ubuntu onto the flashdrive and have gotten it to boot fine. I get prompted to choose what drive to install ubunto onto. I only see an option for my entire HDD. I want to make sure I am only wiping the flash drive and not the actual mac hard drive. Do I continue? Any help is greatly appreciated.


Thank you,
Anthony