Home Page Product Thumbnails have gap inbetween. How to fix?

Hi

my website is http://www.thegemcanvas.com

I have 3 questions.

1) There are gaps between my product thumbnails on the main page.
I tried changing thumbnail size but it doesn’t work. I don’t think that is the problem.

Have anyone encountered this before?

Is it something wrong with the coding? It seems like it’s structured as a 3 column table of some sort. Where do i find the code for this?

2) How do i add images to my slider?

3) At the top right hand corner there is a picture of a shopping cart, the URL linked to it is wrong. Where do i find the code section to change this?

Thank you so much for your help in advanced!! ^_^