Everybody has a bad day, and some days are not good days to be bad days ... (hmmm ...).
It‘s doubly unfortunate that you were only taught some of the stuff too late (i.e. AFTER you wrote the test) - an abject lesson in why it‘s a good idea to finish school first (but, I digress ...)
When I was in recruiting (a long time ago) it was explained to me that mathematics is very important in the testing procedure (since every part of the military needs to work with numbers - bullets, bombs, or torpedoes). Accordingly, since you mentioned you hadn‘t learned some of the stuff until after writing the test, we can assume your math results were not as good as they might have been (and therefore, it‘s entirely possible this portion of the test dragged down your overall score).
A tough lesson to learn, I concede - but, it‘s better to learn it at a young age as opposed to later on in life when you‘re trying to support your family. Ultimately, you‘ll see this is just a speed bump on the highway of life ...
Hang in there.
P.S. (I guess I should confess - I was a math whiz in high school, even winning the senior math award in Grade 9, which meant I beat the Grade 13 students, too. I was 19 when I applied, and in second year university - a huge difference between that and grade 11)
"There is always inequity in life. Some men are killed in a war and some men are wounded, and some men never leave the country ... It‘s very hard in military or personal life to assure complete equality. Life is unfair ..."
John F. Kennedy
"A young man who does not have what it takes to perform military service is not likely to have what it takes to make a living."
- John F. Kennedy