Also its not the end of the world if you don't get a cadetship before starting uni.
Plenty of jobs are avalivle during first year and subsequent years, and generally the only requirement is your at uni and have good grades. Considering some of you are talking about high 90s atars, you've still got many opportunities ahead.
I mean if you miss out this year, join clubs and volunteer and work on doing well during your first year. You may not get the traditional big 4/mid tier cadetship, but there's a bunch of smaller firms that hire undergraduate that would loveeeee to have you.
Just don't give up. Apply for all possible jobs and if that isn't good enough, work on improving the areas you like skills on over the next year to get a position.
Even if you decide not to go for a cadetship next year, you'll still (hopefully) have great marks, great EC's and be more confident when it comes to internship and graduate programs.