Your site is simple to use. This is good. It also means that users won't need much help before they are proficient. But by reducing the screen width, you're punishing your users forever. You can solve this by teaching users about the interaction up front. Try placing some text somewhere on the screen that encourages users to swipe. You can hide it once they've done it once. Alternatively, shortly after page load you can animate the page to peek the next column of content. It will require a little playing around so that the instruction is clear but unobtrusive.