50 minutes is plenty of time to answer the questions if you are reasonably well prepared for the exam. Some of the questions can be answered within a few seconds, others will take some thought or some calculations. Every question has the same numerical weight, however. Don't spend 10 minutes trying to remember how to calculate a solar angle at the expense of answering several easier questions. Read each question very carefully.
Many students make errors because they skim a question and just look for a related answer.
This won't work in this course. For example, if the question asks about something in the southern hemisphere, I have probably included an answer about the northern hemisphere as one of the wrong responses. To succeed in a science class, you really do need to keep up throughout the semester. A fairly intensive review the day or evening before the exam IS a good strategy, but not at the expense of sleep. Group study should be in addition to individual study, and not replace your individual preparation.