Your main HTML page has no closing </head> tag or an opening <body> tag so there may be inconsistencies when your web page is being rendered by different browsers.
Check your page with the W3C Markup Validation Service and fix any errors reported.
Also, your content is within a container whose width has been specified absolutely as 1300px which accounts for the scrolling required to see the right-hand side of your web page on a small screen. Try a smaller value or perhaps a percentage, eg. 100%.
Also, you could try setting your gallery's dimensions to 100% x 100% (if they are not already) and then set the size for the gallery via the gallery's parent container. Being 100% x 100%, the gallery will fill the parent container completely.
SimpleViewer Support Team