At a first quick glance, why such skimpy margins?
(Checked the JPEG. For some reason the PDF was classified as "Unsafe to download.)
If you need space to fit more content, you should decrease your body text size. It generally looks too large, and inconsistent. Those margins and gutters need increasing drastically, for both technical (if it's going to be perfect bound), and aesthetic reasons.
But to be honest, pointing out specific problems isn't the most helpful thing to do. What you really need is a lot more experience and understanding of editorial design. It's more of a science than other forms of graphic design. Grids, type hierarchies an lots of other elements need to be established into some kind of system before you go ahead and design individual pages.
Is this professional work or college assignment?
In regard to margins, pick up a few magazines in the store, and look at how the margins are set on those. I think that 1/4 inch would be a minimum, with the gutter margin being from a half-inch to an inch.
Good to see another South Australian on the forums!
Have had a look at the sample pages that were uploaded and concur with my peers here - the margins from the trim edge of the page to the type are far too small. The design is OK if you're producing a publication for a tablet, but in print there are tolerances of 1-3mm. That is, if you design a page with type that is close to the trim edge, expect to have type cut off, or margins that don't align properly.
Also, proof-read your document (NOT just spell-check! For example, on the contents page you have "panty" instead of "pantry"). The TOC references pages that are in the 300+ range... that's a massive magazine... on 113gsm pacesetter satin it'd be nearly 2cm thick. If it is only for a concept, that's fine.
I also agree that you need to use a more structured framework for your layout. I'd recommend watching some videos from Nigel French on Lynda.com - Training, tutorials & online classes by expert Nigel French - his advice is spot-on and in general, things that he would do - I would do.
The margins are too small for two reasons:
1. Esthetics. A lack of white space looks cramped. Such a cramped design sends a "cheap" impression.
2. Practicality. Printing presses and cutters - especially those used for cheap stuff - do not go exactly. There could easily be a 1/4" (6mm) variation in where the page is cut. This is the real reason why even the cheapest material does not go so close to the edge.