I agree, Calc may not really help you much. I took it but then took a couple of years off from school, and then went back to finish up my degree by the time I was finishing and taking the MCAT I couldn't remember a darn thing from Calc. My physics was trig based and was plenty for MCAT prep. I think the calc thing may have to do more with whatever major you choose....your bio dept may require it.
If you're only a freshman you have time, so just relax and little and focus on doing well in your classes. Some other sciences that you might look into taking later on may be ones such as Genetics, Psychology, Microbiology, Anatomy/Physiology, Immunology, etc... I would recommend going to the websites of some med schools you might be interested in, AND/or going to your advisor or pre-med advisor (if you have one) and getting a list of science classes that most med schools require, and just keep that list in the back of your mind so you can start crossing those off over the next couple of years.
In general:
- Do well in your classes. A "B" or something early on isn't going to hurt you, but if medical school is really something you want to do it'll be much easier if you realize that now and focus on doing well. Take it from me, it's hard to come back from slacking off your first 2 years in undergrad.
- Volunteer: Get involved in pre-med group on campus if there's one since they'll probably have ongoing service projects you can help with. If there's not one just go get involved somewhere. Call a local Senior Center or Nursing home and offer to come in a couple hours a week to spend some time with the residents. Or call up a local hospital and see if you can come in once a week or so and play with kids on the pediatric ward, etc....
- Shadow/Clinical experience: You've already done some it seems. Call up local doctors and see if they'll let you come shadow. Or if you're really interested in a certain field see if you can work out a schedule where you come in and shadow like once a month or something so you get a little more on-going face time with the doc. Could always help in that you could get a good LOR at the end.
- Research: Probably the most variable of all of these. Not "required" but kind of depends what sort of med school you'd like to go to. I helped out some neuroscience research my last year of undergrad (no papers or anything) and quickly found out that basic science research was NOT for me. Will probably look into doing some clinical research this summer, but at least I found something that didn't interest me, which is just as useful. So if you think you'd be interested in research go look up what your professors are working on and if something catches your eye go talk with them and see if you could help out.