Everyone will probably be nervous about starting 3rd year. I was when I started it and I'd like to think I'm very comfortable talking to people etc. Chances are, there will be loads of others in the same boat if you asked them about it.
3rd year is fun (not as fun as 4th year/speciality year IMO), but still fun. As has been mentioned above, with 3rd year, your aim should be to take a very good history by the end of each rotation, and certainly by the end of the year. You will hear variations of the the phrase "60/70/80% of the diagnosis is from the history" or "listen to the patient, they are telling you the diagnosis", and both of these points are actually very true! Spend time on the wards clerking patients - if nothing is going on, pop down (with a clinical partner) to A&E to clerk some new patients and present them to one of the junior doctors or even one of the final year med students on the ward. Pick good tips up from the doctors/nurses/other medical students you see and incorporate them into the way you carry yourself: the way they communicate with patients, the way they present a history to a senior, the way they prioritise tasks, the way they speak to patients' families etc. This all forms part of the "informal curriculum", i.e. what you're not explicitly taught by anyone but are expected to know at the end of medical school.
Having said that, balance the hospital work with the book work - I found that quite difficult to do initially as I was in awe of the all the options open to you as a clinical medical student, so would spend almost all my time there doing random jobs (which obviously has its perks), but spent very little time actually reading around the subject for the written exams. Yea, erm, don't do that. Once you get that balance between ward work and book work, I actually found clinical years more exciting (and easier to revise for) than pre-clin years. Learning things in context aids a lot with recall for the exams.
It may take a while to get used to being so independent and deciding how you chose to spend your time (the timetable is a lot less rigid than in pre clin), but once you get into the swing of things and into a nice little routine, you'll be fine. Most people prefer clinical years anyway so chances are you'll be in that majority.