The number of columns is related to the maximum width value, which you can also adjust in the template settings.
You have configured a max width of 1200 pixel for 7 columns. This results in a width of approx. 172 px per product. The content area of your page is 960 pixels wide. 960 divided by 172 gives space for 5 columns. If you reduce the max width setting to 900, you will get 7 columns. 🙂
[asa2_feed tplid=”17″ image_size=”small” max_row_items=”7″ max_width=”900″]3[/asa2_feed]
Just play a bit with several combinations of max_width and max_row_items to get your preferred layout.
As mentioned earlier, feed limits above 10 don’t make sense as feeds currently only support 10 items (the top 10 delivered by Amazon’s RSS feeds).