Mentoring: find YouTube videos from MiMentor and any of the school admissions offices. LMSA and SNMA chapters too. Read
Building Your Best School List - SDN .
Volunteering: i would suggest finding something, yes. I don't know who runs community gardens where you are living but that is one way to combine your interests with a service orientation.
I think you should ask your network for advice on self identification too. I understand not getting pigeon holed into certain presumptions about your life -- past or future -- based on your heritage. Include it if it fits your narrative for sure.
In researching for Becoming a Student Doctor, i have learned a lot more about "registering" and some if its problems. With that insight, I don't push as hard on this. Similarly for not being Spanish fluent if you are Latinx. (One will need to enroll in the course to know more.)
You should find a lot of the UC schools to be very receptive about your story and hopefully your intentions to become a physician. Network and figure out your comfort level with each group of administrators, faculty, students, and clinical opportunities. You have the potential that I can say, "Make them want you."