Felix
The real purpose behind the correct use of grammar and spelling is make your point in as clear a manner as possible, leaving no room for misinterpretation or ambiguity. This has proven to be vital on more than one occasion, particularly when legal brethren are involved!
A very useful skill, but not one I always adhere to on here
Some advice that may be of use:
1) Be careful of malpropisms, though, make sure you know what a word actually means before you use it!
2) Speak to the AFCO, they are the recruitment channel and are usually fairly 'in the know'. Any difficult questions can, and indeed are, referred to OASC.
3) Have the fortitude to resit, if that is what you want to do. Don't for a minute, however, assume that it will be an easy ride to:
a) convince your teachers that you deserve a complete re-start, and;
b) re-sit, thinking that you have been through this already and that you know everything.
4) Have a clear goal (which you seem to have), a plan of how you are going to get there and, most importantly, support that plan with facts from the authoritative source.