Slider and Mask Sizes

Hi all,

I am having an issue getting a slider to display only three slides and hide the rest, while still being centered in the middle of the screen.

I am confused as to what the settings (both size and overflow) need to be for the mask and the slider itself to make this happen.

I only want it to display three slides at a time like the image below in the middle of the screen, but currently, the slides are taking up the full width of the page. Thank you in advance!

Here is my site Read-Only: LINK

Any ideas on this one? - Thanks!