what would you like to change? if you have too many items, you obviously can't have them fit in one line. I believe you also said you were going to be adding more.
You can try installing a mobile navigation plugin. You can set the width for it to start displaying at the point where your navigation wraps to two lines.
There are several in the plugins. Find one that looks easy for you to use. http://wordpress.org/plugins/search.php?q=mobile+menu&sort=
Or you can allow two lines of navigation. It's not "wrong" to display that way. The important thing is that is easy to find and that the links work for all devices. (hover drop downs do not always work on touch screens)