Mega menu width and column

Hello,
i followed the video to create a mega menu. I’ve 9 links to show under the mega menu with 9 photos. I would like to have it all on the same row and once the row is filled to begin a new row without centering the images.
Actually you can see that the “scopri i nostri prodotti” menu link have 3 images per column with really a lot of border around.
Is it possible to modify this borders and to augment the number of columns of the mega menu? Actually the max number is 6, after that the other images will create a new row and will be centered for all the width of the row.

Than there is another problem. I guess is related to the z-index of the mega menu.
Once you are into a product (woocommerce page) eg and you move the mouse on the “scopri i nostri prodotti” you will see the mega menu appear. Once the megamenu shows if you move to the left column (that’s over the big image of the product page) you will see that the product page image will prevale and the megamenu will disappear.

Let me know :)
Thank you