I have set up a layout grid in the category item layout

leading count:1
columns for leading: 1

Primary count:4
columns for primary:4

I have only 1 category in the menu and 5 items in the category.

The Primary columns for primary 4 appear in one column (one under the other)
I have tried everything but cant find a way to set them up to be one next the other in 4 columns.

I would like it to be responsive so if using a mobile device they will appear one under the other.

can you please help.

I'm using K2 v2.6.8
and joomla 3.3

You are not loading K2's default css, or your template does not support K2.
You can enable K2's css in the extensions parameters.

Great thanks mate. I have enabled K2's default css and getting the "columns for primary:4 " working now.

how can I set them to be responsive? so on mobile they will appear one under the other?

Something like this will do the trick.
Paste it in your template's stylesheet or override K2's template.

Instead of 35.5625em you can use a pixel value like 768px.

More on overriding can be found here: getk2.org/documentation/tutorials/174-templating-with-k2-and-the-concepts-of-sub-templates