Let me preface this by saying I haven't been in your situation, but I don't think you should let it get in the way of your goals. While volunteering is great experience, I think you should consider nixing the volunteer jobs and for now and through the summer getting a second job to try to pay off as much of your debt as you can before you get into school full-time. There will be time yet to volunteer, and while experience is a really important part of your application, logically speaking, I think it's more important to try to improve your credit score.