Medical school exams are designed to meet standardised outcomes. Unless your med school has an unusually high attrition and failure rate, or its graduates consistently struggle to gain full registration, you'll almost certainly learn what you need to learn. This isn't to say that the curriculum must be perfect and there's no need for improvement, but if other people are succeeding there's no reason why you shouldn't be one of them.
Secondly, I think you're catastrophising here. I obviously can't speak for your med school, but I've never heard of anywhere that has no formal teaching in clinical years. As part of our clinical induction we got a tour of the hospital education block, which has a lecture theatre and seminar rooms as well as the simulation suite. There were students from a higher year using those rooms when we visited. So I doubt that placement means you'll never have another lecture again. I also think that at transitional points (e.g. preclinical to clinical year, final year to F1) people naturally tend to be more focused on their areas of weakness, which causes them to perceive the demands of the next stage as greater or at least very different from what they really are. I seriously doubt that anyone is going to expect a medical student on placement to single-handedly identify a rare arrythmia, for example. (Or to suture with confidence - a very kind surgical demonstrator had to remind me that I was getting way ahead of myself when I panicked over that!) What we can be expected to do is join dots. To go with your resp example, the main conditions we were taught about in our resp cases were COPD, asthma, and interstitial pulmonary fibrosis, but when sepsis came up in infectious diseases a few months later we were able to piece together a lot about the respiratory problems commonly seen in these patients using info about respiratory physiology that we already had. It's important to get confident at reasoning from what you know, which really will be more than you think.
There's always going to be a significant amount of uncertainty with medicine, no matter how we're taught. Our experience will be partly determined by the patients who happen to be on the ward on a given day, and it would be impossible to ensure that we all saw exactly the same conditions in similarly-presenting patients. This uncertainty is compounded by the fact that as GEM students our experiences already vary a lot. My cohort has someone who worked in health economics and statistics, former paramedics, and someone who was involved in a surgical research project. We all take different things out of every lecture or clinical situation depending on our background, which influences the questions we ask, the information that stands out as most memorable, and the things we prioritise. At first I felt as if I was at a massive disadvantage because my own background seemed much less relevant than some of the other students'. I felt I was playing catchup all the time and learning less than everyone else. It took me about eight months to discover that this isn't actually the case. It's common to underestimate what you're learning and to develop a sort of academic FOMO as a result, and as I said, I have a feeling this is probably worse at transitional points. We need to actively challenge these thoughts rather than just assume they're true.
I'll give an example of what I mean. I had three learning outcomes that I needed to get signed off, one of which was taking a history, and supposedly one day to do this in. I was assigned to theatres in the morning and to ICU in the afternoon. Taking a history isn't exactly feasible when the patients you're seeing are unconscious, intubated, or both, so I parked that idea and concentrated on learning what I could. I asked the anaesthetist lots of questions about pharmacology and practised writing a few mock prescriptions for the meds that patients often need after surgery. In ICU I had a conversation with the reg about the psychosocial needs of longer-term patients and how these can be met in the critical care setting. I have a background in mental health, so I was very interested in this side of things. Eventually I thought about how I could get my outstanding sign-off, and emailed my tutor to suggest that I pop in to ED at some point next week - there are always so many patients needing triage that it shouldn't be too difficult to get a history. This is what I meant when I spoke about being proactive. It's not about being a bubbly extrovert who tap-dances down the ward (I'm definitely not that!). It's about looking at each situation and thinking, "OK, what could I learn from this?" and being pragmatic in how you address any problems that do come up. There's no reason why a quieter person can't be just as effective at that as a more extroverted one.