Mobile Issue using Catch Responsive

Hi Wondering if you can help me please - I am new to all of this and am currently trying to create a website (no url as I am in test mode) using Catch Responsive Free. It has all been working fine until I click on the mobile icon at the bottom left - in this view I get a horizontal scroll bar across the bottom of the screen - should it not all fit on the screen like it does on the tablet icon? I have disabled all plug-ins and removed all custom css (of which there was very little anyway) taking the website completely back to the bare bones but it is still happening. Please could you advise Thanks