I am also in the medical field and I very much understand where you're coming from. If you are studying medicine, I would highly recommend that you attempt to expose yourself to the field when you are a student. I say this because when you graduate and start your career, you will STILL be learning new things every day. It is absolutely a lifelong learning situation. At least if you start working in the field as a student, you will get used to asking questions. Also, getting exposure to the medical field early on as a student, allows you to see some very 'grey areas' of medicine, which involve ethical decision-making with your healthcare team.
I empathize with you about the idea of 'throwing yourself' into the field for practice (giving shots, etc). The term 'throw yourself in' is very very intimidating!! I want to reassure you that EVERYBODY starts out not knowing what the heck they are doing, especially when it comes to medical procedures as simple as giving a flu shot. It will take time and practice, wherein you will develop your skills and increase your confidence.
(Mainly because I'd have to ask around to know how to sign up, and ask for help, and be subject to judgement as a result of lack of skills, or awkward ways of asking for help since I don't feel comfortable doing so).
I also want to emphasize that it will not be easy at first. You WILL ask a lot of questions, but it is better to ask than to be ignorant of what you should be doing as a medical student. I have to admit that I get more anxious around healthcare professionals who act like they know everything, but they really don't. They became too afraid to ask questions, and this is obviously dangerous for the patient receiving medical care.
Try to take things step by step. Learn one procedure at a time if it works for you best. Once you master that step, you try another procedure and so on.
All the best to you! (((hugs)))