Partitioned my mac, deleted the partition wrong. Installed OSX on external volume, how to reset mac from there?

My hard drive was pretty cluttered before this, but anyways lets move on. I installed windows and was having issues with it, so I deleted it through disk utility. After I did that, I read I was supposed to do it through boot camp. Crap, now I'm stuck with a missing partition that my computer thinks is still there. I have OSX installed on an external hard drive ready to use, how do I reset my mac completely from there. I have everything backed up on another external drive that I use for all my backups so I don't run the risk of losing everything if something goes wrong. I tried doing all the keyboard commands that are supposed to bring up the reset menu like holding down option upon start up, but I have to do it like that just to turn my computer on. Please help me.