I've got a crappy old samsung a3 and my website looks fine - there's no sideways scrolling, it fits perfectly width-wise.

But now I've got a new phone, with a much higher resolution, and the website doesn't fit - it scrolls off the edge of the screen and has a horizontal scroll bar.

Is there something I'm doing wrong? How do I fix it...? I thought BP was supposed to adapt to the screen width.

ps. It's definitely the mobile version.