Hmm let's calculate by the age shall we?
if you retake O level's Maths and other subjects, it is at most
1 year and subsequently additional 3 years to poly or 2 years to A
Levels. Then a degree.
If you go ITE, you will spend a few years(not sure of time
needed to complete ITE cert), after that a poly, then perhaps
degree.
If you take private, you end up still need to clear maths as I
believe it is a core subject to pass. Still need 1 year.
From the options you have, I strongly suggest you to spend 1
year to retake O levels. 1 subject is fine, but better to clear a
few more at the same time, just to widen your choice.