What can a student who works hard,is motivated to learn do to improve his grades? Background:
I am from Nepal (neighbouring country of India). So, our education system is different even though the syllabus is similar to the west. Majority of our grades come from final semester examination. The questions asked in exams are mostly repeated from the last 5 years(10 questions papers i.e every year 1 Regular and 1 Supplement exam). The exams are relatively far easier compared to what it would be in the west, BUT here is the catch. The teaching is below par, culture of reading reference book is rare among students, mainly because less time for students to be able to do so. So, what it does is that you put x hrs in class for the sake of attendance(75% attendance is a must to pass the class), you learn nth in those x hrs and you study for another y hours, first trying to  learn the basic that you should have got in the class and again trying to actually solve old questions.
Problems:
I am in engineering. It is worrying because-:
I like studying.
I don't memorize much, I study to learn.
I study very hard. I put lots of hours in study.
I even solve old questions during these 3 days exam gap.
How I study?
During semester, I properly do assignments, I do much of the assignments by myself.
During 3 days exam gap I buy a note that consists old questions solutions. Then I put my assignment notes and laptop in front  of me. Then I start to solve old questions by using notes solutions and internet videos. I solve last 5 years(only 5) of questions and other related questions that have not came in 5 year(only 5). For eg-: If there is a question &quot;what is aquatic animal&quot; I also study topics related to &quot;what is terrestrial animal&quot; and &quot;what is aerobic animal&quot;.
History:
I have always got great marks in exam. Be it 90%+ in SLC and 87% average in +2. People think I am rattu tota (Hindi/Nepali for parroting from memory) who memorizes everything, but no I don't memorize anything.(But yes I use mnemonic techniques to remember).
What could my problems be?
(This is what I feel but I am unsure if they are really the problems)?
Whenever  I like some subject, I study almost everything related to that topic. Turns out, questions mostly come from last 5 years and not much from too much of the past. Since I dedicate more time to 1 topic, it makes less time for other topics. And if hard questions come from those topics I put less time, then you know I will do bad in that subject.
I have found that I do good in subjects that I find hard rather than subjects that I find easy(irrespective of if the subjects are meant to be hard or easy).
Also I always feel that if I studied 3-4 hrs more in the exam study gap, I could have scored better. i.e It would make up time for my revision and I could score better marks. (Even though I do active recall after solving every old questions).
At this moment, I am genuinely frustrated, extremely frustrated. I am dedicated, all teachers get surprised when they see my final marks, and I am actually learning something and not memorising.
Can you suggest anything for me?
I think your difficulty is with prioritizing tasks and committing to them. Don't worry, it is not uncommon, and its easy to solve once you accept it.
First, you need to decide which is more important to you at present, doing well in the exam or learning the subject well.
(Obviously learning the subject well is very important, but the exam grades may be a more immediate and pressing concern. Possibly they impact future prospects significantly, or maybe they are not so relevant). If the exam is important now, then be strategic about it. The deep appreciation of the subject should have started earlier, and if it didn't, you should revisit it once you get through the exam. If the exam isn't so important, then relax and keep enjoying the subject.
Second, about topics to study. A few days before the exam is not the time to play favorites with topics. At that point it shouldn't matter what you like or don't like (again, this is something for either before or after exam week). So spend an appropriate amount of time on each topic. A lot of students spend more time on topics that are graded heavier - this I personally detest, but it is strategic and meets a short-term goal.
Finally, mnemonics and active recall (I'm not familiar but this sounds a bit of voodoo) and the like are probably best left behind in school. I know it takes some pain to change mindset and the way you approach subject matter, but there is a reason university is distinct from school. Sure, use mnemonics when they are a standard tool (colors on a resistor for instance), but don't use them to start committing regular subject content to memory. Even if you have understood the topic well, this will serve as an unhealthy crutch that you'll keep falling back on, and will feel helpless without.
Apologies for being a bit blunt, but one of the distinguishing skills of a university education is realizing that we are responsible for our condition and our actions alone can improve them. Its certainly not late to start seeing that.