Graduate program interview?

Prepare a three minute (maximum) verbal presentation-of-self that explains why you want to go to graduate school and what you hope to accomplish with an advanced degree. This is a question that was presented to me in a letter when my interview date was scheduled. I know this should be self-explanatory, but I'm having difficulty with it because I tend to ramble when given that much time to speak. The perfectionist in me causes a lot of unnecessary anxiety. lol. Any advice? My ultimate goal is an MSW/PhD in Social Work.