When I was a senior in college someone called the tutoring center I'd been going to for all four years. Even though I had cross-country practice most saturday mornings, I'd go to the Catholic Center for Saturday tutoring when I got out early. I told them I couldn't commit to it in the spring but to call me if they got really busy...you could never tell how many kids were going to show up.
Anyways, the tutor director was a '5thyear' masters student I'd been working with all through college. When some kid applied to Pritzker at the UofChicago (where we were) the admissions office called to ask if this kid really did volunteer. She waited to ask me about him and I'd never seen or heard of him either. The admissions office then gave us his student id picture. Nope.
I always wondered if that kid ever learned why he didn't get his interview.
Don't lie. It's really not cool. You should work in your community because its important to you. It's one thing to volunteer so you can say you volunteered...its another to lie about it.
Just my opinion,
Sarah