I would read the Engineering Journal Rubric so you can create your own opinion, but I’ll also say mine.
(I’ve put the key details in bold 
)
You want to aim for quality over quantity. But as part of the rubric it wants you to record as much of the engineering process as you can (to the point where someone else can refer to the notebook and make the robot themself) - but this contradicts quality over quantity.
I would recommend making sure you don’t repeat yourself or include unnecessary details, instead of trying to cram it down. This could be drafting what you want to write about first, then cutting it down. Or limiting yourself to a page a session.
What I wouldn’t recommend is re-writing your previous 300 pages, as the journal is ideally written along with the process while your doing it, so you may lose points for re-doing it. But maybe I’m just being overly cautious.
As long as you write meaningful stuff that isn’t too repetitive, I wouldn’t worry about how many pages it takes up.
I’m not sure how the judging process works, but I’m pretty sure they wouldn’t read the whole journal, so I don’t see what difference it makes. As long as there isn’t any fluff, and the information they are looking for is easy to find.
That’s probably the biggest problem; a long journal makes things hard to find, especially physical ones. This season I switched to a digital journal and it has allowed me to create link to reference other pages, and the contents, it allows the judges to easily find what they are looking for.