If your website is not displayed correctly in mobile version, please check the following options:
The default Jimdo mobile version ( design> mobile view ) in custom layout should be deactivated as shown in screenshot:
In Settings> Edit Head section you should have 3 links. Please make sure you haven't deleted them:
<meta name="viewport" content="width=device-width, initial-scale=1"/>
<link href='https://fonts.googleapis.com/css?family=Barlow:300,400,500,600,700,800' rel='stylesheet' type='text/css'>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css"/>
If your website is not responsive, you might have made an error in CSS. In this case you need to replace the original CSS files