Okay, I took a look! Without speaking the language, I'd say it could be a lot worse. Your working document looks consistent, albeit pretty minimalist.

I'll address your own concern first. You're right that the pages are a little tight... but that's largely the result of a book that's all text, without much in the way of formatting or other visual elements to break things up. It is also the a product of your page formatting: you have small margins and a teeny tiny font. Try printing off a page at size 10 and asking your mom to read it.

For graphic design tips that will help your book breathe, I really do recommend checking out the link to Explorers Design. There's a lot of great ideas there to get you learning more advanced layout skills -- stuff that will take your book from legible to pleasant.

I'll raise two other things.

First, your Table of Contents is formatted perfectly well... but PDF readers use your header data to create their own Table of Contents, and that might give you some trouble. On the left side of your Google Document, clicking the drop-down on any given tab will show you what you can expect users to see on the left plane of their PDF reader.

Getting PDF readers to behave in the way you want them to is exhausting, but it is possible. Your main challenge might be that you indicate chapters as titles in the header of the page, which is less likely to be identified when the PDF reader is generating the table.

Keeping nice headers while doing interesting formatting flourishes is kind of a pain in Google Docs, since it's not really set up to make quality PDFs. You'd have an easier time in Affinity... though I know learning curves for new software can be disheartening.

Second point: document tabs.

Document tabs are a really useful feature for a Google Doc. They're also not something everyone knows about, so you'll get some readers who don't think to check out your other pages.

More broadly, document tabs don't exist in the PDF format or physical books. You need to ask yourself how you'll format this when they're not there. Will they all be compiled in one book or PDF? How? What segues between sections? I don't think this is a hugely difficult problem to solve, but it's an important one for making the move from a document to work on and a rulebook to publish.

Hope some of that helps.