[Please help] Products only show on 2 colums at Shop page

This is my problem, you can see in my pic is products only show on 2 colums. How to fix it? Please help, i need fix it soon.

p/s: I'm not good English, so... i hope you know my problem. Thank you so much!

 

My site: http://sumire-store.com/shop/

 

i found and edit here, so, my problem have fixed.

in style.css, i edit margin and width.

Code:

/* Shop Product Single Page Style
========================================================*/
.content-bar .site-content ul.products li#product_item{
float: none;
display: inline-block;
vertical-align: top;
margin: 0 18px 25px 0;
position: relative;
width: 28%;