I'll throw my little story in here in case the OP is reading - always helps to have multiple points of view.
I did alright in primary school[1] but mentally checked out in the first year of high school (year 7). I actually told my mum not to waste her breath chastising me for poor marks: I was more interested in friends and socialising so I wouldn't be doing much on the school front. She should expect Ds. not Fs necessarily, but D average. She was kind of taken aback but gave me the benefit of the doubt.
In year 11 I changed schools (common in Canberra where I went to high school, and Tasmania where I went to college which is what they refer to year 11 and 12 as, it's the last 2 years of high school when you're 17 and 18).
The school I went to in Tasmania was incredible (word up Friends' School!) and I had amazing teachers. I caught up and got good grades in (almost) all areas except for one crucial one: Maths.
See all the other classes like English, Psychology, Sociology, Japanese, to a lesser extent Chemistry and Physics, weren't cumulative. Maths, on the other hand, builds each year on what you learned the year before, so the fact that I had been actively ignoring maths for the past 4 years meant I had no hope of catching up. So I got a pass. I didn't fail, but I got a 7 out of 20 so pretty close to failing.
The fact that I passed and the fact that I went to school in Tasmania meant that I could use the Maths course I did as a pre-requisite when applying for a Mechatronics degree when I was 21 (the final year in which I was able to use my tertiary entrance score!).
Why I chose to do an engineering degree I have no idea. I didn't really think too much about how Maths heavy it would be. I just thought that Mechatronics sounded really cool. I didn't even really understand what it would entail.
The 1st year, I failed (yes, actual fail, like 32 out of 100) all my Maths courses. Didn't even come close to passing a single one.
I then took 2 years off and deferred while I went to the UK and worked for 1.5 years in London as a programmer. I had taken 6 months of C first year, and really loved it - it was the only class I did well in that year.
So I worked and a funny thing happened: I got a job I wasn't even remotely qualified for, and through a trial by fire realised that I could learn things, and then use them, completely independently. I did this professionally before I ever did it in an academic setting.
The first year of university, and these 1.5 years following it, taught me, basically, to RTFM.
So when it came time to go back to University for 2nd year (by now I was 23) I took 6 months to study my high school Maths text books at my own pace. I did all the exercises, asked some people I knew for help when I couldn't figure something out, basically, learned Maths the same way I had realised that I could learn how to program on the job.
I then went back and passed (with low credits) all the subjects I had failed in 1st year, and then passed all my 2nd year Maths (and Maths related) courses (some of them I even almost got distinctions - like 72 out of 100!)
I was so pleased with myself. I was so pleased with that fact that I'd learned how to learn, that nothing could ever have hurt my sense of pride in those marks, even though all the kids around me were depressed because they got a 90 instead of a 95.
The moral from this for my purposes (may or may not apply to you) was:
If you start from behind, you might never catch up in terms of the absolute value of your outcome (ie. I think there is virtually zero chance that, unless I was some sort of crazy genius, that I could have truly aced my Maths exams 2nd year of uni). BUT ...
Your sense of achievement at learning how to learn can, if you let it, overshadow that shortfall AND ...
That is the most valuable thing you can learn anyway: the most valuable skill (and the one I look for most when hiring people) is the ability to read and parse a complex set of instructions without freaking out. This is the essence of all learning, and regardless of what mark you come out with, you can count yourself lucky if you figure out how to do this. It's incredibly valuable.
The secret of life: RTFM.
[1] I'll be using Australian school terminology.