I'm sure you realize your GPA is below that of the average matriculant but your higher MCAT may correct for that. Sorry to break it to you, but schools aren't really going to cut you any slack because you went to a top 10 undergrad.
Unfortunately, volunteer work is not really optional anymore and if you haven't already done so, I would try to start accumulating hours as quickly as possible. Since your application is already late in the cycle, you may want to try and do some volunteer work this year and re-apply next year. Shadowing is less important and since you're already pressed for time, you shouldn't worry about it too much.
You should consider asking those lab professors for recommendations anyway even if you didn't get a publication. Most applicants actually don't have publications but still have decent LORs from their supervisors.