Quote from page 14 of the “Ballot paper formality guidelines” published by the AEC on 14 August 2023:

Senate guidelines
Consecutive sequence of numbers – Above the line
For an above the line vote (ATL), voters are instructed to consecutively number at least 6 boxes above the black line, in the order of their preference, commencing with the number ‘1’.
[…]
However, where a voter consecutively numbers fewer than 6 boxes, (including only one box with a first preference) the ballot paper will still be formal, but will exhaust after the last consecutive number.

In other words, if you only numbered 5 boxes above the line it does still count, it just exhausts sooner.

Their practice voting tool has sensibly omitted the finer details, they always encourage people to vote “correctly”.

Regardless of you definitely won’t make the same mistake next time I’m sure.