Aim to get to uni. Don't start thinking about other ways yet. Leave that for a last resort.

Course pre-requisites in WA (probably change between states) are something like three of:
Calculus
Applic maths
Chemistry
Physics

Thats what I did along with some form of english. It was a reasonable workload, but manageable. The thing that killed me was english...
You can't become an engineer through an apprenticeship, unless you want to get into fabrication or something like that.

I have no idea how it works in other states, but the Tertiary Entrance Rank (TER) for most forms of engineering is around 84 here. I scraped in with 86...
If your worried you won't get a high enough score, do another easier TEE subject (like an easier TEE maths) just to boost your marks. (they calculate your TER using the four best marks) If you can manage calculus, then an easier math will be a pushover.

Good carreer choice. Which section of engineering are you thinking of?
The world will always need more engineers...