4 Column Site with 3 Subcategories, move products down

I have my site set to 4 columns for products. For one product category, I have 3 subcategories. The way it is showing, it’s starting the product list on the same line as the category line, like so (C is a category, P is a product):

C | C | C | P
P | P | P | P

and so on.

I want a break after the 3 categories so it’s displayed like this:

C | C | C
P | P | P | P

and so on.

I can’t find any actual help on the web – all the tutorials given are old and break the site.