Gerard
I can't comment on SA as I don't know the score out there. If it's any help, here in the UK (with a very large aviation industry) your school results have very little bearing on your employability. It's all relative though.
If you are applying to be sponsored by an airline then you need a good education (because you will have very little else to offer at the tender age of 25ish) and they will use it as a filter.
Now, if you did as I did which was to work in industry for 10 years and prove yourself to be a capable individual before self funding your licence and then applying to the airlines then your education (or lack of it!) has little relevance........as long as you can pass the assessment tests that everyone has to sit.
Generally speaking, you have more to offer the employer due to your greater life experience, especially if you have got off you behind and gone and done something outside of the work environment as well........I served in the reserve forces for 11 years and gained invaluable leadership/ teamwork and many other skills beside.
So there you have it. My suggestion would be to enhance your profile by doing something other than education/ work whilst you are training and then you have so many more 'life skills' that you can offer a potential employer. This way you have something extra that will make up for any perceived weakness elsewhere (but do practice the maths so that you have no problems with the entry tests!) Teamwork is a huge one with airlines here in the UK so anything that proves that you have these skills is a big bonus.......you know, boy scouts, rugby coaching a youth team, outward bound instructing etc etc. Get the idea?
As for your flying abilities being 'pretty good', well an airline will give you a sim assessment if they want to test your flying skills before offering a job, so, that is what you have to pass. However, I don't thing being 'ace to base' in the sim will get you the job offer if you fail the maths test (if there is one), or the English test, or the aptitude test or the interview! You see it's the whole 'rounded individual' that they want, no good being a good stick and rudder merchant if you can't interact with the various team members that all need to work together to ensure a Safe, On-time, Good service airline.......................
I can only assume that an SA airline would be recruiting similar types as pilots to UK airlines.
I wish you well Gerard.
PP