ML upgrade process freezes, help please!!

Hey, I have a MBP 13" mid 2012, and I was just trying to upgrade from Lion to Mountain Lion. Just about 12min to finish my Mac completely froze. I had to force a shutdown while pressing the power button. Now I turned it on and the Installer popped up and now it trying to install it again, I hope it doesn't freeze again. I'm realy scared (hopefully I have a back up).