I'll be the dissenter with the caveat that I wouldn't shadow if you had something better you could be doing with your time.
Personally, I think now (and thought when a premed) that shadowing was a useless way to spend time and it was nothing more than "checking off a box" that adcoms expected you to have checked. I realize adcoms expect you to have done some shadowing, so do it at some point. You won't learn anything substantative that will help you in med school. Call me a cynic, but you're just not in a place to benefit from shadowing as a premed. I really don't think many people entering med school even really get what being a doctor is, not for lack of trying, but because it's just really hard to get it without being immersed in it. You can't get that from a couple hours a week.
You certainly don't have enough time to do any decent research. If you need the money, I would try to find a part time job either in the medical field or tutoring. If you don't need the money, volunteer doing something you're passionate about - you'll get much more (and be more likely to stay committed) if you get involved in a volunteer project that you can really get behind.
Good luck.
