Aye, don't be disheartened.
Maths = concept + speed.
That's all you need. Speed wise i believe you have put in quite
some effort since u said u worked hard i presumed you've done quite
a bit of practice.
Concept wise, you must be able to sieve out the very
fundamental-sort of like a generalisation to various problems
instead of seeing every question as an individual problem.
Consult your prof immediately if you get stuck with certain parts
of the course, it's ok to be shameless and ask alot of question. If
it helps you can study together with your friends then can discuss
with each other oso.
Ultimately, uni is not just about working hard, you gotta know what
to work hard at. A blind mugger isn't what the society needs hence,
it's not what the uni will provide.
P.S. i oso NTU 2nd year haha