line break or change mobile under 600px

Any way to make it break in half when the page size gets to 600px and below?

This looks great until browser width gets about 550 pix, then it gets a little funky, and at 360px width it causes a horizontal scroll bar to appear and lots of white space, as I have lots of pages.

Would be cool to have an option to make it change to drop down menu at certain pixels, in may case I think 550 or so.

Even a css for max-wdith or something.

any ideas?