It may depend on where you plan to apply but I think that 60 hours is more than enough. Spend some time as a volunteer at a place where you can talk with and serve patients (hospital, hospice, home-hospice, free clinic, nursing home) so as to show that you can interact one-on-one with the sick (not just watch someone do it). You might also want to consider research (next summer at the latest) if you have your sights set on a top 20 research school. (Not officially required but many schools wind up with 89% of students having research experience so you figure it out -- best odds, have research and volunteer or paid work face to face with patients along with the shadowing).