As a TA, I used a Scantron machine a handful of times. A small tear on the side likely won't affect how your answer sheet is graded.
If you're absolutely paranoid, just have them manually grade it, as @"Cant Get Right" suggested.
@J.Y.Ping @"Dillon A. Wright" Please enter me on this lottery! I have been posting that I was interested but my name isn't showing up on the lottery list. I am desperate to get into one of these.