I don't have that much volunteer experience -- maybe fifty hours or so (I couldn't do it over the summer because of transportation issues), but I have 80-100 hours of shadowing and I'm a Health Aide at Northwestern (which is kind of clinical experience -- your peers are your "patients"). Therefore, even though I don't have tons of volunteer hours, I feel I have enough other clinical experience to make up for it. It looks to me like you're in the same position -- three years of paid clinical experience is a lot, so if you really hate your volunteering job, I think you'll be ok. However, make sure you have other non-medical community service experiences (tutoring, soup kitchen, etc.) to show some sort of altruism to the adcoms. If you have that, I think you should be fine.