I logged in for one last time to say this as I was in a similar situation and your IQ is not to blame. Don't know if it helps but here's some tips you need to know;
1. Studying becomes a lot easier if done in groups (round/conference table) in a proper and comfortably air conditioned room. Information, Assignments can be shared with "friends" and your workload can be reduced. Exchange of feedback between group members on difficult questions or assignments will be useful for you.
2. Don't study sitting on the floor/ground like these fags, remember you're in STEM, not liberal arts. Proper upright posture is needed to maintain optimal blood flow to your brain, it also improves concentration or focus. Sit on a proper and comfortable (not too comfortable) chair and large enough desk/study without clutter.
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3. Remember, depression, anxiety and procrastination are killers, they contribute to one another and follow a cyclic pattern. Depression hinders your learning ability 10 fold, anxiety fuels procrastination. Overall, emotions kills or inhibits focus and learning ability. So, try to suppress all negative emotions as much as possible. I don't know how, but removing all sorts of distractions (social media) might be a good start.
4. Make a properly scheduled study plan and prioritize what you need to learn to ace the exams. Don't study more that what's required of the syllabus/exam, many times, the professors or instructors may hand out few tips for the exam if he's generous. If a topic is taking a lot longer (3 times more) than expected, move on to other topics and come back to this one later on. Don't worry about study taking more than 20 hrs, its nothing tbh, the people who have passed the exam without opening a single book are either liars, or cheaters, or tipsters (relying solely on tips and luck) or Einstein level IQ (very rare/not believable). I knew of such people in college.
5. At least, test yourself to the bare minimum of 10 previous semester's exam papers (5 of them untimed first, the remaining 5 timed). See how well you do. You can then use the results as a gauge to determine the probability that you'll do the same in the real exam.
6. Eat well, avoid junk food, drink plenty of water, sleep and wake up on time, don't drink alcohol, you can smoke to reduce anxiety if you're a smoker.