Please make sure you select the correct number of pages to be bound. I can bind up to 350/360 pages at a time, anything more than that will be split into sections.
If you have more than 350 pages, please adjust the quanity before checking out to meet the amount of pages you need bound. 
I use a plastic comb for binding. Please note that due to the curve in the comb, the pages may not sit evenly in the comb.