You sound exactly like me last year before I started clinicals. Being reserved is not necessarily as negative a quality as you may think. It can project a thoughtfullness, self-control, and humility that I feel other students lack. However, you need to make a good impression on faculty and unfortunately you cant just walk around with your step1 score on a piece of paper and so it only works if you answer questions, and participate in the group discussion. While I wasn't the most talkative person on my team, I was always the first person to volunteer to do any task, regardless of how menial. This may seem like a small thing but its noted by attendings and residents. So you have to be very proactive, no one is going to really tell you what to do in clinicals, you have to make yourself useful.

With regard to patient communication, the only way to improve is to talk to patients, which can be very difficult at first, and its okay if you forget things and even have to go back to them for followup questions. The only way to improve here is to spend quality time with patients. I've seen students go into a patient's room for 5 minutes, fire off questions as fast as they can just to get it over with. Don't be like that, this is the time in your career where you don't have 25 patients to take care of, only a handful, so make the most of it and sit down with them and really get to understand whats going on with their health. Being reserved I think really helps here the most, if you show that you are listening, care about what people have to say then they will open up to you and it will be easier to remember their HPI, PMH etc. The best way to impressive an attending or resident is to show that you know everything thats going on with the patient's care.